DESCRIPTION OF MICROWAVEBENCH MEASUREMENT OF FREQUENCY AND WAVE LENGTH 2. REFLEX KLYSTRON MODE CHARACTERISTICS 3. CHARACTERISTICS OF ISOLATOR 4. MEASUREMENT OF SWR (DIRECT METHOD) 5...
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LCRT2010ST LG Microwave Service Manual MFL06272518
Department of Electronics & Communication Engineering
Manual and Observation Book Microwave Lab By K!rid"ar #a$u wwwengglabsblogspotcom
K!rid"ar #a$u
wwwengglabsblogspotcom
2
K!rid"ar #a$u
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Department of Electronics & Communication Engineering Microwave Lab
wwwengglabsblogspotcom Department of Electronics & Communication Engineering
Microwave Lab "ame of t:e stu;ent< stu;ent< Class '*E< Roll "o<
%ca; -ear<
*%DE!l %o
%ame of t"e E/periment
Date Conducted
4
*nitials of staff
K!rid"ar #a$u
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5
K!rid"ar #a$u
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DE!C#*.+*O% O, M*C#O0(1E BE%C2
:e Microwave benc: available available in t:e lab is ;esigne; to accommo;ate / = ban; signals ranging from 7*2 to )2*1 .:>* % t?pical Microwave benc: consists of t:e following bloc@s*
It consists of an electron gun* Electrons are liberate; from t:e cat:o;e w:en t:e cat:o;e is :eate;* '? means of focussing electro;es t:e electrons are ma;e to form into a t:in beam* :e beam is accelerate; accelerate; towar;s towar;s t:e cavit? w:ic: :as a :ig: :ig: voltage applie; to it* :e electrons overs:oot t:e .ap in t:is cavit? an; travel towar;s t:e repellerB repellerB w:ic: t:e? never reac:B reac:B as t:e repeller is negative negative wit: respect to t:e cat:o;e* Electrons Electrons in t:e beam reac: some point in t:e repeller repeller space an; are t:en turne; bac@B eventuall? eventuall? be ;issipate; ;issipate; in t:e ano;e cavit?* cavit?* If t:e voltages are a;uste; t:e returning ret urning electrons give g ive more energ? to t :e gap t:an t:e? too@ from it on t:e out war;* It will be assume; t:at oscillations are able to start t:roug: noise or switc:ing transients* Let us see :ow t:ese oscillations are maintaine;* :is is ;one b? ta@ing specific electrons passing t:e gap at t:e selecte; instants*
:e reference electron ? comes to t:e gap w:en t:e R# voltage is >ero an; going negative* Electron ?F as before passes t:e gap wit:out being affecte;B travels towar;s t:e repeller an; eventuall? returne; to t:e ano;e wit:out :aving touc:e; t:e repeller* :e closeness closeness of its approac: is governe; b? its velocit? w:en it emerge; emerge; from t:e gap* :us fast electrons electrons come closer to t:e repeller repeller t:an slow ones an; t:erefore ta@e a longer time to return return to t:e resonator resonator gap t:an t:an electrons electrons w:ic: ;i; not 7
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approac: t:e repelller repelller so closel?* closel?* :e electronF electronF AF w:ic: passes t:e resonator gap slig:tl? before t:e reference electron electron encounters encounters positive positive R# voltage* In t:e absence of a gap voltage electron AF woul; t:en :ave returne; to gap before t:e reference reference electron ?F* 'ut because of t:e positive R# voltage w:ic: is present in t:e gapB at t:e time electron AF reac:es t:e gap electron electron AF will be accelerate; accelerate; an; so it goes to t:e repeller more closel? t:ere b? spen;s more time in t:e repelller before returns to t:e ano;e* 'ut because electron AF :as starte; earlier t:an t:e reference reference electron electron ?FB t:ere t:ere is ever? ever? c:ance c:ance t:at it woul; woul; catc: catc: up wit: electron electron F?F w:ile w:ile returni returning* ng* Similarl? Similarl? electro electronn >F w:ic: w:ic: :as starte; starte; later later t:an t:an refer reference ence elec electron tron ?FB ?FB encoun encounters ters negative negative R# voltage voltage** So its velocit? velocit? will be less t:an referen reference ce electron electron ?F* ?F* So electron >F spen;s less time in t:e repeller repell er space compare; to reference electron ?F* %s electron electron >F :as starte; starte; later later t:an t:e referenc referencee electro electronn ?FB ?FB t:ere t:ere is ever? ever? possibilit? possibilit? t:at it can catc: up wit: electron ?* In fact all t:e electrons w:ic: reac: t:e gap w:en t:e rf voltage is c:anging from maAimum positive to maAimum negative voltage will catc: up wit: one anot:er an; form into a bunc:* #or eac: R# c?cle one bunc: will be forme;* +#(%!*+ +*ME #or oscillations to be maintaine;B t:e transit time in t:e repeller space or t:e time ta@en for t:e reference reference electron electron from t:e instant it leaves t:e gap to t:e instant of its returnB returnB must :ave t:e correct correct value* :e most suitable suitable ;eparture time is obviousl? obviousl? centere; centere; on t:e reference reference electron electron is at t:e )79 9 point of t:e sine wave voltage across t:e resonator resonator gap* :e best possible time for electrons electrons to return to t:e gap gap is w:en t:e t:e voltage t:en eAisting across t:e gasp will appl? appl? maA maAimum imum retar;at retar;ation ion to t:em* t:em* :is is t:e time w:en gap voltage voltage is maAi ma Aimu mum m posi positi tive ve** %s s:ow s:ownn in t:e t:e %p %ppl pleg egat atee ;iag ;iagra ram m in or;e or;err to ma main inta tain in t:e t:e oscillations t:e ransit time s:oul; be G n H c?cles n integer MODE!< :e transit time obviousl? ;epen;s on t:e repeller an; ano;e voltages an; so t:ese voltages s:oul; be properl? a;uste; a;uste; to give t:e correct value of transit time* $:en t:e transit time satisfies t:e euation G n H c?cles t:e electron electron bunc:es will be retar;e; maAimum so t:e power will be maAimum* $:en t:is euation is not satisfie; t:e oscillator oscillates wit: less power*
8
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,ig #efle/ klystron mode c"aracteristics
% combination of %no;e an; Repeller voltages ;etermines t:e transit time* Instea; of c:anging bot: ano;e an; Repeller voltagesB voltagesB we @eep t:e ano;e voltage constant an; var? t:e Repeller voltage* $:en t:e transit time G n H c?cles is satisfie;B satisfie;B t:e power will be maAimum ot:erwise ot:erwise t:e @l?stron @l?stron oscillates oscillates wit: less power as s:own in t:e figure* figure* Eac: value value of nF is sai; to correspo correspon; n; to a ;iffere ;ifferent nt refleA refleA 0l?stron mo;e* :e earlier t:e mo;eB t:e larger t:e output power* oltages reuire; are :ig: to operate t:e 0l?stron in earlier mo;es* :is lea;s to :ig:er power ;issipation an; :ence lowere; efficienc?* If t:e cavit? is correctl? tune; an; a suitable voltage is applie; to t:e ano;eB an? one of t:e available mo;es ma? be pro;uce; b? a;usting t:e repeller voltage as s:own in t:e t:e fig* fig* It is seen t:at maAimum output is obtaine; obtaine; w:en nF G 2* 2* %lso for an? mo;e in a refleA @l?stron maAimum power is obtaine; w:en t:e repeller voltage gives t:e eAact reuire; value of transit time toget:er wit: t:e ano;e voltage w:ic: is @ept constant* constant* $:en t:e repeller is on eit:er si;e of t:e correct value B t:e out put power is less t:an t:e maAimum* % c:ange c:ange in t:e repeller repeller voltage c:anges t:e freuenc? freuenc? of oscillations oscillations slig:tl? as s:own in t:e fig* %ssume t:at t:e freuenc? of oscillations is )9.:>* :e perio; of eac: c?cle is )99psec*$it: mo;e 2 in use t:e transit time G 2*64A )99 G 264 psec* If t:e repeller voltage is slig:tl? ;ecrease;B t:e transit time will be increase; slig:tl?* Let t:e )9
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transit time :as become 264*24 psec* Instea; of oscillating at )9.:>Bwit: a slig:tl? ;iminis:e; ;iminis:e; powerB t:e @l?stron @l?stron will oscillate oscillate in suc: suc: a wa? t:at t:at 2 c?cles of time perio; perio; will be increase; slig:tl?B an; so t:e freuenc? freuenc ? will be ;ecrease;* :e new freuenc? will be 8*88) (>* Mec"anical tuning
:e cavit? ;imensions ;imensions ;etermine ;etermine t:e freuenc? of oscillations oscillations of t:e @l?stron* @l?stron* :e cavit? ;imensions are varie; b? fleAing a portion of t:e cavit? wall or b? c:anging t:e space of t:e cavit? gri;s* :is t?pe of freuenc? tuning is @nown as mec:anical tuning* Electronic tuning
%s ;iscusse; earlier w:en t:e repeller voltage is varie; in an? mo;e t:e freuenc? of oscillations varies slig:tl?* :is is @nown as electronic tuning* Electronic tuning sensitivit? is given b? ES G f 2 = f ) J v2 = v) M(> J volt $:ere f 2 an; f ) are t:e freuencies in M(>* %t w:ic: mo;e power falls to :alf of its value at t:e top* Modulation in klystron
% simple t?pe of mo;ulation mo;ulation is a suare wave %mplitu;e %mplitu;e mo;ulation mo;ulation internal internal @nob provi;e; in @l?stron @l?stron power suppl? suppl? pro;uce; pro;uce; b? mo;ulating mo;ulating t:e reflector reflector voltage*:e voltage*:e internal mo;ulation mo;ulation is usuall? usuall? a suare wave mo;ulation mo;ulation of freuenc? freuenc? about 799K2999 799K2999 (>*:e amplitu;e an; freuenc? can be varie;* $:en t:e RefleA @l?stron is operate; in I" mo;ulati mo;u lation on mo; mo;eB eB S$R meter meter is is use; use; as t:e output output meter* meter* $:en $:en t:e @l?stron @l?stron is operate; in C$ continuous continuous $ave $ave mo;e a ;c micro ammeter of range range 9 to )99 )99 m% m% is use; as t:e output meter* #epeller protection
It is essential to ma@e sure t:at t:e repeller of a @l?stron never ;raws current b? becoming positive wit: wit: respect to to cat:o;e* cat:o;e* !t:erwise it will will ver? rapi;l? rapi;l? be ;estro?e; ;estro?e; b? t:e t:e impact of :ig: velocit? electrons* % cat:o;e resistor is use; to ensure t:at repeller can not be more positive t:an t:an t:e cat:o;e* cat:o;e*
))
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Klystron .ower !upply
0l?stron power suppl? is some w:at ;ifferent ;ifferent from or;inar? ;c power suppl? owing to specific operation oper ation of t:e @l?stron tube* :e ;esirable features featu res are< )* :e suppl? must be more stable an; regulate; as compare; to usual amplifier or oscillator power suppl? at lower freuencies because small variations in accelerating potential ma? result in ;e tuning of t:e @l?stron* @l?stron* 2* Since @l?stron freuenc? freuenc? is a function of t:e repeller voltageB voltageB it s:oul; be well regulate; an; free from ripples* 3* It s:oul; suppl? mo;ulation as per reuirements* 0l?stron tube reuires t:ree ;ifferent ;ifferent voltages to generate microwave power* :e 5*3 ac suppl? is given to t:e :eater of t:e electron gun* :e beam voltage is a;ustable from 299 to 199 olts wit: negligible negligible ripple voltage* :is voltage can be rea; from front panel panel meter calibrate; calibrate; into voltage voltage an; current* current* '? c:anging c:anging t:e in;icator in;icator switc: we can fin; fin; t:e curren currentt ;rawn ;rawn b? t:e t:e @l?stron @l?stron tube tube w:ic: w:ic: is betwee betweenn 29 to 19 m%* m%* :e reflector voltage is applie; to t:e repellerB w:ic: can be varie; from =29 to =2)9 ;c wit: respect to cat:o;e* :e internal internal mo;ulation mo;ulation is usuall? a suare wave mo;ulation mo;ulation of freuenc? about 799 to 2999 (>* :e amplitu;e an; freuenc? can be varie; from t:e front panel @nob provi;e; in @l?stron power suppl?* suppl?* Resonator cavit? itself is maintaine; maintaine; at groun; potential potential an; becomes t:e reference reference for measuring measuring all ot:er voltages* voltages* 0nob is provi;e; to operate t:e @l?stron in C$ mo;e or %M mo;e* In C$ mo;e we use micro ammeter as t:e output meter* *solator
It often :appens at microwave freuencies freuencies t:at coupling must be strictl? a one wa? affair* affair* :is applies for most microwave generators w:ose output amplitu;e amplitu;e an; freuenc? ten; to fluctuate ver? significantl? significantl? wit: c:anges in loa; impe;ance* %s a result result some some means must be foun; foun; to oin oin a generat generator or to t:e loa; in suc: a wa? t:at t:e coupling is uni;irectional uni;irectional from generator generator to loa;* Isolator allows t:e signal in one ;irection ;irection onl? an; ;oes not allow t:e reflections reflections to reac: t:e generator* generator* #errites are use; in isolators an; circulators* % ferrite is a nonKmetallic materialB w:ic: :as magnetic properties similar to t:ose of ferrous metals but resistivit? resistivit ? so :ig: as to ma@e it an insulator* i nsulator* Manganese ferrite an; inc ferrite ferrite are some of t:e ferritesB ferritesB w:ic: are commonl? commonl? use;* %s all t:ese materials materials )2
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are insulators em waves can propagate t:roug: t:em* 'ecause t:e ferrites :ave strong magnetic magnetic properti propertiesB esB eAternal eAternal mag magneti neticc fiel;s fiel;s can be applie; applie; to t:emB t:emB wit: several several interesting resultsB inclu;ing t:e #ara;a? rotation* $:en an em wave travels t:roug: a ferriteB an R# magnetic magnetic fiel; is applie; to t:e materialB materialB at rig:t angles to t:e
;irection ;irection of propagation propagation if t:e mo;e of propagation propagation is correctl? c:osen* If an aAial magnetic magnetic fiel; fiel; from a permane permanent nt mag magnet net is applie; applie; as wellB wellB a com compleA pleA interaction ta@es place in t:e ferrite* $it: onl? t:e aAial ;c magnetic fiel; present t:e spin aAes of t:e spinning electrons align align t:emselv t:emselves es along along t:e lines lines of force force * $:en $:en t:e R# mag magneti neticc fiel; fiel; ;ue to t:e propagating propagating EM waves is also applie; B it is perpen;icular perpen;icular to t:e aAial ;c magnetic magnetic fiel; so t:at electrons precess about t:eir original spin aAis* :is :as t:e effect of rotating t:e plane of polari>ation polari>ation of t:e waves propagating propagating t:roug: t:e ferrite* :e amount amount b? w:ic: t:e plane plane of polari>ati polari>ation on of t:e waves will will be rotate; rotate; ;epen;s ;epen;s on t:e lengt: an; t:ic@ness of t:e ferrite material an; on t:e strengt: of t:e ;c magnetic fiel;* :e isolator consists of a piece of circular wave gui;e carr?ing carr?ing t:e E )) mo;e B wit: transitions to a stan;ar; rectangular gui;e an; E )9 mo;e at bot: en;st:e output en; transitions transitions being twiste; t:roug: 14 9 * % t:in pencil of ferrite is locate; insi;e t:e circular gui;eB an; t:e wave gui;e is supporte; b? a permanent magnet generates a magnetic fiel; in t:e ferrite* 'ecause t:e ;c magnetic fiel; is applie; B a wave passing t:roug: t:e ferrite in t:e forwar; ;irection will :ave its plane of polari>ation s:ifte; cloc@wise t:roug: 14 oB b? t:e time it reac:es t:e output en;* en; * :is was t:en passe; pass e; t:roug: t:e suitabl? suitabl ? rotate; )3
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output B an; an; it emerges emerges wit: an insertion insertion loss loss between between 9*4 to ) ;'* % wave t:at tries to propagate propagate t:roug: t:e isolator in t:e reverse ;irection ;irection is also rotate; cloc@wise B because t:e ;irection ;irection of #ara;a? rotation ;epen;s onl? on t:e ;c magnetic fiel;* :us w:en t:e wave emerges out from t:e input transitionB it is absorbe; absorbe; b? t:e resistive vane but also it can not propagate propagate t:roug: t:e input rectangular rectangular wave gui;e because of its ;imensions* ;imensions* C*#C7L(+O#
It also ma@es use of ferrite ;evice an; often :aving four ports* It :as t:e propert? t:at eac: terminal is connecte; connecte; onl? to t:e neAt cloc@wise terminal* terminal* :us port ) is connecte; connecte; to port 2 but not to ports 3 or 1* Port 2 is connecte; connecte; to port 3 but not to ports ) an; 1 an; so on*
(ttenuators
%ttenuators %ttenuators are use; to provi;e suitable power level* En; tapere; resistive car;s are place; parallel parallel to t:e electric fiel; to attenuate attenuate it in case of fiAe; attenuatorsB attenuatorsB w:ile in variableB variableB eit:er t:e pa; area is re;uce; or orientation orientation of t:e car; is c:ange;* c:ange;* :e a attenuators use car;s or loss? ;ielectric materials* %ttenuators are of two t?pes* )* #iAe; %ttenuators %ttenuators 2* ariable ariable %ttenuators Matc"ed Load
:e ;evice w:ic: w :ic: :as an eAcellent matc:>ero reflection an; an ; complete absorption absorp tion of al l t:e power inci;ent on itB is calle; a matc:e; loa;* % simple form of matc:e; )1
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loa; in wave gui;e is a piece of resistance resistance car; place; in t:e wave gui;e parallel to t:e electric fiel; as s:own in fig*
:e front front of t:e car; car; must be tapere; tapere; so t:at it presents presents no ;iscont ;iscontinui inuit? t? to t:e microwave signal* If t:e car; is long enoug: to absorb almost all of t:e powerB powerB t:e reflections reflections from t:e far en; will be sufficientl? sufficientl? small so t:at t:e net reflection reflection is negligible* I f t:e car; :as a 29;' of attenuation in one ;irection an; so t:ere is a two wa? attenuation attenuation of 19;'* %n? loss? material can be use; as a matc:e; loa; in a wave gui;e gui;e as long as provisio provisionn is ma; ma;ee to avoi; avoi; reflecti reflections ons from t:e front front en;* en;* Materials commonl? use; for soli; soli; loa;s are loss? ;ielectricsB ;ielectricsB ;ielectrics ;ielectrics loa;e; wit: carbon or pow;ere; metalB woo; B san; etc* Cavity Meter
Cavit? meters are use; to measure or to stan;ar;i>e stan;ar;i>e t:e freuenc? of oscillations oscillations of a microwave s?stem* :ere are t:ree t?pes of wave meters* )* ransmission t?pe< :ese :es e pass t:e signal to w:ic: w :ic: t:e? are tune;* 2* %bsorption t?pe< :ese attenuate onl? t:e resonant freuenc? of t:e signal* 3* Reaction t?pe< :ese absorb energ? from t:e transmission line resonant freuenc?*
)4
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K!rid"ar #a$u
In an absorption t?pe cavit? meterB w:ic: we :ave in our labB if t:e signal freuenc? euals t:e resonant freuenc?B freuenc?B a portion of t:e signal will be absorbe; an; we observe a ;ip in t:e out put meter* $:en t:e signal freuenc? is not eual to t:e resonant freuenc? t:e signal will not be attenuate;* #ectangular wave guide
% rectangular rectangular wave gui;e consists of four con;ucting con;ucting walls* :e ;istance between t:e two si;e walls walls is ;esigna ;esignate; te; as aFB w:ic: w:ic: is t:e broa;er broa;er ;imensio ;imension* n* :e ;istanc ;istancee between t:e top top an; bottom bottom walls is t:e smaller smaller ;imension an; an; is ;esignate; ;esignate; as bF* In a stan;ar; rectangular rectangular wave gui;e b G aJ2* In a rectangular wave gui;e eit:er E or M mo;es are possible* EM wave ;oes not eAist* In case of E t:ere will not be electric electric fiel; fiel; along along t:e ;irecti ;irection on of propagat propagation ion an; for M t:ere wonFt wonFt be magnetic fiel; along t:e ;irection ;irection of propagation* propagation* Depen;ing Depen;ing on t:e t?pe of mo;e use; a wave is represen represente; te; as E mBn or M mBn* Integer F mF represents represents t:e number of of :alf waves of electric fiel; intensit? intensit? variations variations along t:e t:e broa;er broa;er ;imension of t:e rectangular wave gui;e an; t:e integer nF represents number numb er of :alf wave intensit? variations along t:e narrow wall* % rectangular wave gui;e acts as a :ig: pass filter allowing :ig: freuenc? freuenc? signals an; attenuating attenuating t:e low freuenc? freuenc? signals* 2 λ = :e cutoff wave lengt: m + n a b If t:e free space wave lengt: l is less t:an λc B t:at signal will propagate* propagate* If λ c
2
2
eual to or greater t:an λc t:at signal will not propagate* :e cutoff freuenc? f c is eual to v c J λc B w:ere vc G 3A)9)9 cmJsec Dominant mode
Dominant mo;e is t:e mo;e for w:ic: t:e cutoff wavelengt: is maAimum* E )9 is t:e ;ominant mo;e in rectangular wave gui;e* #or E)9 mo;e λc G2a w:ere aF is t:e broa;er ;imension of t:e wave gui;e #or /F ban; rectangular wave gui;e $R89 aF G 9*8FF G 9*8 A 2*41 cms* So t:e cutoff wavelengt: λc G 2 A 9*8 A 2*41 G 1*462cms* :e relations:ip among t:e t:ree λs is given b? ) J λ2
G ) J
λ g2
H )J
λc
2
)5
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K!rid"ar #a$u !lotted !ection
o sample t:e fiel; stan;ing waves in wave gui;eB a narrow longitu;inal longitu;i nal slot wit: en;s tapere; to provi;e smoot:er smoot:er impe;ance impe;ance transformation transformation an; t:ere b? provi;ing provi;ing minimum mismatc:B mismatc:B is mille; on t:e top of broa;er wall* Suc: section is @nown as Slotte; wave gui;e section* section* :e slot slot is generall? generall? so man? wavelengt:s wavelengt:s long to allow man? minima of stan;ing wave pattern to be covere;* covere;* :e slot is suc: t:at it ;oes not muc: influence t:e fiel; configuration* !n t:is section a probe a small metallic ro; for provi;ing electric coupling inserte; wit:in a :ol;er is mounte; on a movable carriage* :e output is connecte; to a ;etector an; in;icating meter* :e slot slot in a slotte; section must be cut in suc: a wa? t:at no appreciable appreciable power lea@s out of t:e line* In a wave gui;e t:e slot is cut in t:e center of t:e broa;er wall an; is parallel parallel to t:e line of propagation propagation parallel to t:e current lines at t:e center an; so it causes negligible negligible interference interference wit: t:e current lines an; :ence t:ere will not be an? ra;iation from t:e slot*
,ig !lotted !ection Crystal diode
:e simplest an; most sensitive ;etecting ;etecting element is a microwave cr?stal* It is non linearB linearB non reciprocal reciprocal ;evice w:ic: rectifies rectifies t:e receive; receive; signal an; pro;uces pro;uces a current proportional proportional to t:e power input* Since t:e current flowing t:roug: t:e cr?stal is proportional proportional to t:e suare of t:e voltage it is referre; as a suare law ;etector* ;etector* :e suare law ;etection propert? of a cr?stal ;io;e is vali; at low powers below )9 mw* (owever at :ig: an; me;ium power levels t:e cr?stal gra;uall? becomes becomes a linear ;etector* ;etector* o un;erstan; un;erstan; t:e action of t:e ;io;e consi;er consi;er t:e euation of its current = voltage c:aracteristics I
$:ere
e& = IS eAp − ) @
Is G Saturation current )6
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K!rid"ar #a$u
I G Current correspon;ing to voltage @Je G Constant w:ose value is between 9*924 to 9*93 micr microw owav avee ener energ? g? is is repr repres esen ente te;; b? G 9Cos ωt Bw:ere 9 is t:e pea@
If
voltage*
I
e& Cos ω t = IS eAp 9 − ) @
e& Cos ω t ) e& Cos ω t I = I ) + + + − − − − @ @ 2 Since 9 NN @JeB neglecting t:e :ig:er or;er terms 2
9
9
S
I
I
=I
e&9 Cos ω t S
=I
@
e&9 Cos ω t
S
2
+I
S
2
2@
2
+I
S
@
) + Cos 2ω t + 2
2
e &9
2
2
e &9 2
1 @
2
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e &9 Cos 2ω t 2
1 @
2
+
KKKKKKK
:e above euation suggests t:at at low microwave powers 9 NN @JeB t:e current t:roug: t:e cr?stal is proportional proportional to t:e suare of t:e barrier voltage* :e ;c current component in t:e above eApression is given b? I ;c
= IS
e 2 &92 1 @ 2 2
% ;c ammeter reects t:e freuenc? freuenc? components components an; measures t:e ;c current onl?* onl?* :e cr?stal ma? also be for ;emo;ulation purpose w:en S$R meter is use; as t:e output meter* Suppose t:e input signal is amplitu;e mo;ulate;B it can be represente; b? ) ) & = & Sin ω t + & Cos ( ω t + ω t ) + & Cos ( ω t − ω t ) C
c
2
S
c
s
S
2
c
s
$:ere w
is t:e carrier freuenc? an; w is t:e mo;ulating freuenc? c s being t:e carrier wave amplitu;e amplitu;e an; t :e mo;ulating wave amplitu;e c s %ssuming t:at t:e ;etector is operating in t:e Suare law region 2 I G@ I
= @ [ &C2 Sin 2ω c t ] + @ [ &s2 Cos 2 ( ω c t + ω s t ) ] + @ [ &s2 Cos 2 ( ω c t − ω s t ) ] + 1
1
)7
KKKKKKK
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K!rid"ar #a$u I
&2 &2 &2 = @ C + S ( Dc current ) + @ &C &S Sin ω s t ( mo;ulating signal) − @ S 1 1 2
Cos 2ω s t ;istortio n + :ig: fre
If t:e terms ot:er t:an t:e mo;ulating signal be filtere; using appropriate filters t:e cr?stal wor@s as a ;emo;ula ;emo;ulator tor * (owever t:e ;istortion ;istortion is alwa?s alwa?s present present an; for t:is :ig: ,F in;icating instrument suc: as S$R meter is nee;e;* "ote< $:en t:e signal is not mo;ulate; mo;ulate; C$ mo;e a ;c ammeter of range 9 to 49 micro amperes is use; as t:e in;icator* ;c current measure;
I ;c
= IS
e 2 &92 1 @ 2 2
$:en a signal s ignal is mo;ulate; suare law mo;ulation a S$R meter is use;* Current measure; I G Sin w t s c s Direct rea;ing S$R meter is a low noise tune; amplifier volt meter calibrate; in ;b an; S$R for use wit: Suare law ;etectors* % t?pical S$R meter :as a stan;ar; tune; freuenc? of )999(>B w:ic: is a;ustable over a range of 4 to )9 O for eAactl? matc:ing in t:e source mo;ulation freuenc?* :e ban;wi;t: of t:e amplifier is also a;ustable from )4 to )39 (>* 'ot: cr?stal an; bolometer bolometer ma? be use; in conunction conunction wit: t:e S$R meter* meter* :ere is a provision provision for :ig: 2499 to )9999 o:ms an; low 49 to 299 o:ms impe;ance cr?stal inputs* 1!0# ME+E#
8E%E#(L .#EC(7+*O%! +O BE +(KE% +(KE% *% +2E L(B
)* 'efore 'efore ?ou switc: switc: on t:e @l?stro @l?stronn Power suppl? suppl?BB @eep t:e repelle repellerr voltage voltage @nob in its maAimum position* #irst ?ou appl? t:e repeller voltage an; t:en onl? t:e beam voltage* voltage* If t:e repeller voltage is @ept minimumB t:ere is ever? c:ance t:at t:e electron beam can :it t:e repeller repeller lea;ing to instabilit? instabilit? of freuenc? of oscillations* oscillations* :oug: necessar? precaution precaution is ta@en to see t:at t:e repeller will alwa?s be negative wit: respect to cat:o;eB cat:o;eB it is a;visable a;visable to @eep t:e repeller voltage maAimum negative negative w:en ?ou switc: on t:e @l?stron power suppl?* 2* Do not appl? appl? t:e t:e beam beam voltage voltage prior prior to t:e t:e repelle repellerr voltage* voltage* 3* Switc: on t:e cooling cooling fan fan before before switc:ing switc:ing on t:e @l?stron @l?stron power power suppl?* suppl?*
)8
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1* Put an isolator isolator alwa?s alwa?s between between @l?stro @l?stronn oscilla oscillator tor an; rest rest of t:e set up* :is :is isolates @l?stron tube from reflections* 4* :ere :ere s:oul; s:oul; not not be an? air gap gap at t:e t:e unctio unctionn of two wave gui;e gui;e components as t:ere will be loss of microwave power* 5* %ll t:e rea;ings rea;ings s:oul; s:oul; be ta@en ta@en un; un;er er maA maAimum imum power power con;itio con;itions* ns* :at :at is after switc:ing on t:e @l?stron power suppl? @eep t:e repeller voltage constant constant to aroun; 399 olts* Decrease t:e repeller voltage ma@ing less negative an; observe t:e ;eflection in t:e output meter* ar? ar? t:e reflector voltage till t:e ;eflection ;eflection rea;s maAimum* $:en S$R meter is use; as t:e output meter t:e signal s:oul; be mo;ulate; mo;ulate; aroun; )999(>* In t:is case we :ave to var? t:e amplitu;e amplitu;e an; freuenc? freuenc? of t:e mo;ulating mo;ulating signal till t:e ;eflection rea;s maAimum in t:e output meter* 6* :e beam current current s:oul; s:oul; not eAcee; 39 m%* If t:e beam current current is greater greater t:an 39m%B turn off t:e suppl? an; c:ec@ t:e voltages* 7* #or accurate accurate measurements measurements of S$R use eApan;e; eApan;e; scale in S$R meter* meter* 8* Perform t:e eAperiments eAperiments wit: in t:e suare law response of t:e cr?stal cr?stal ;io;e* )9* $:en t:e freuenc? of oscillations oscillations of t:e @l?stron is c:ange; tune t:e repeller voltage ever? time for maAimum response* ))* ))* $:en $:en an ammeter ammeter is use; use; as t:e out put put meter we :ave :ave to operate operate t:e @l?stron @l?stron in C$ mo;e* $:en S$R meter is use; as t:e output meter we :ave to operate it in I"*M!D mo;e onl?* onl?*
29
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K!rid"ar #a$u
E/periment 93
Date Measurement of ,re:uency and 0ave Lengt"
< o measure t:e freuenc? an; wavelengt: of t:e microwave signal generate; b? RefleA 0l?stron oscillator an; to verif? t:e euation
(im
E:uipment <
0l?stron power suppl?B @l?stron mount wit: RefleA 0l?stronB IsolatorB cavit? meterB ariable attenuatorB Slotte; sectionB s:ort circuitB S$R meter* Block Diagram of t"e Circuit <
+"eory <
:e relations:ip among t:e free space wave lengt: B gui;e wavelengt: g an; t:e cut off wavelengt: c is given b? ) J λ2 G ) J
λg2
H )J
:e cut off wavelengt: c is given b?
λ c
=
λc
2 2 2
2
m + n a b
#or t:e ;ominant E )9 mo;e mG)B nG9* c G 2a w:ere QaQ is t:e broa;er ;imension of wave gui;e* #or Q/Q ban; Rectangular wave gui;e $R89 a G 9*8QQ A 2*41 G 2*275 cm c G 2a G 2A2*275 G 1*462 cm*
2)
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K!rid"ar #a$u
:e gui;e wavelengt: g varies wit: respect to free space wavelengt: an; w:ic: is governe; b? freuenc? of oscillations* :oug: t:e gui;e wavelengt: g ;oesnQt ;epen; upon t:e t?pe of terminationB we use s:ort circuit as loa; for getting a clear stan;ing wave pattern* .rocedure< )* %rrange %rrange t:e Microwave benc: benc: as s:own in t:e ;iagram* :oug: t:e values values of an; g ;o not ;epen; upon t:e t?pe of terminationB to get a clear stan;ing wave pattern s:ort circuit is use; as t:e loa;* 2* $:en SJC is use; as t:e loa; because of t:e mismatc: between wave gui;e an; t:e loa;B stan;ing waves are forme; as s:own below*
Load
Towards G e n e t a t o r d s
5
d s
d s
4
3
ds2
d s
1
λ g 2
3* Move t:e probe along t:e slotte; slotte; section an; observe observe t:e stan;ing wave pattern* pattern* $:en t:e probe is at voltage maAimum maAimum position it couples maAimum maAimum rf energ? w:ic: is converte; converte; into ;c current current b? t:e cr?stal cr?stal ;io;e* %s t:is current current is maAimum maAimum we can see maAimum maAimum ;eflection ;eflection in t:e S$R meter* Similarl? w:en t:e probe is at voltage minimum minimum position it couple coupless minim minimum um rf ener energ? g? an; t:e corre correspo spon; n;ing ing ;efle ;eflecti ction on in S$R me meter ter will will be minimum* 1* #iA t:e probe at voltage minimum position minimum ;eflection in S$R meter an; note ;own t:e probe position sa? ; )* Move t:e probe probe to t:e neAt minimum minimum position an; an; note ;own t:e probe position sa? ; 2* :e ;istance between successive minimum points will be eual to gJ2* gJ2 G ;2K;) g G 2;2K;) 4* '? using t:e eApression )J 2 G )J g2 H )J c2 t:e free space wavelengt: can be obtaine;* c G 1*462 cm* %fter calculating t:e value of freuenc? can be obtaine; b? using t:e eApression 22
K!rid"ar #a$u
wwwengglabsblogspotcom f G cJ G 3A)9 )9J cm
5* #reuenc? of t:e signal can also be measure; using t:e cavit? meter* :e resonant freuenc? of a cavit? cavit? ;epen;s ;epen;s upon t:e ;imension ;imensionss of t:e cavit?* cavit?* %s t:e cavit? cavit? is ;esigne; ;esigne; for A ban; freuenc?B its resonant freuenc? can be varie; between 7*2 to )2*1 .(>* In an absorption t?pe cavit? meter if t:e resonant resonant freuenc? f r ;oesnQt eual eual t:e signal freuenc? f sB no power will be absorbe; b? t:e cavit? meter an; t:e signal will be passe; on to t:e neAt section wit:out an? attenuation* If t:e resonant freuenc? f r euals t:e signal freuenc? f sB most of t:e signal will be absorbe; b? t:e cavit? cavit? itself an; t:e power available available to S$R meter will be uite low* low* So a ;ip minimum ;eflection ;eflection can can be be observe; in S$R meter* meter* $:en a ;ip ;ip is is observe; observe; t:e resonant freuenc? f r an; t:e signal freuenc? f s will be eual* :e resonant freuenc? can be measure; b? fin;ing t:e micrometer rea;ing an; t:e correspon;ing correspon;ing freuenc? can be obtaine; using t:e grap: micrometer rea;ing s freuenc?*o fin; t:e freuenc? of t:e signal generate; using t:e cavit? meterB rotate t:e freuenc? meter in anti cloc@wise ;irection ;irection an; observe t:e ;eflection ;eflection is S$R meter* If a ;ip is observe; observe; it means means t:at f r an; f s are eual* #in; t:e resonant freuenc?* freuenc?* :at is not:ing but t:e signal freuenc?* Compare t:e freuenc? measure; using t:e cavit? meter wit: t:e value of freuenc? obtaine; earlier* 6* "ow c:ange t:e freuenc? of t:e signal an; repeat t:e steps to fin; out gB an; freuenc? f of t:e signal* Eac: time measure t:e freuenc? using cavit? meter also* 7* Draw a grap: between )J 2 an; )J g2 an; verif? t:e euation )J 2 G )J g2 H )J c2 is satisfie; or not* E/pected grap" <
23
K!rid"ar #a$u
wwwengglabsblogspotcom
Observations
#ree space $ave lengt:
.ui;e wave lengt: g
#esults & Conclusions
21
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K!rid"ar #a$u E/periment 9;
Date #efle/ Klystron Mode C"aracteristics
(im
< o o ;etermine t:e mo;e c:aracteristis of RefleA 0l?stron oscillator i*e*B Repeller voltage s output current* Repeller voltage s freuenc? of oscillations*
)* $:en ammeter is use; to measure t:e ;eflectionB t:e @l?stron :as to be operate; in C$ mo;e wit:out an? mo;ulation* 2* 0eep t:e beam voltage constant sa? 399 an; a;ust t:e repeller voltage to get t:e maAimum ;eflection in t:e ammeter* %lso @eep t:e attenuation to a ;esire; level*
3* C:ange t:e repelle repellerr voltage voltage in steps of 29 an; note note ;own t:e output current* current* %lso %lso measure t:e freuenc? of t:e signal using t:e cavit? meter* 1* Plot t:e mo;e c:aracteristics as s:own in figure*
24
K!rid"ar #a$u
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,ig* Klystron Mode C"aracteristics +able +able #epeller 1oltage 1oltage vs Output .ower #epeller 1oltage 1oltage vs ,re:uency #epelle ller vol voltage age
Output Cuu Cuurent
25
,re:uency ncy
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E/periment 94
Date C"aracteristics of *solator
(im
< o ;etermine t:e c:aracteristics of t:e given Isolator*
)* #irst connect t:e above circuit wit:out t:e Isolator ' B t:at is wave gui;e ;etector is to be connecte; after t:e cavit? meter* 2* %;us %;ustt t:e t:e repelle repellerr volta voltage geBB %mplit %mplitu; u;ee of t:e t:e Mo;ulati Mo;ulating ng signal signalBB #reue #reuenc? nc? of t:e Mo;ulati Mo;ulating ng signal signal to set maA maAimum imum ;eflect ;eflection ion in t:e S$R meter* meter* %lso %lso note ;own t:e rea;ing of 'eam voltage an; Repeller voltages* 3* :is :is maAimum maAimum ;efle ;eflect ction ion in t:e t:e S$R nee; nee; not rea; rea; 9 ;'* $it: it: t:e :elp :elp of t:e variable attenuator attenuator ma@e t:e ;eflection ;eflection to rea; rea; 9 ;' on ;' scale scale in t:e S$R meter* meter* :at is t:e maAimum ;eflection is now a;uste; to rea; 9 ;' reference level* 1* "ow insert t:e isolator ' between cavit? meter an; Detector as s:own in t:e figure* :at is we are giving t:e signal set to 9 ;' reference level to port ) of isolator an; measure t:e ;eflection on ;' scale of S$R meter* 4* Interc:ange t:e ports of Isolator ' B t:at is given t:e signal of 9 ;' reference to port 2 an; connect t:e ;etector to port ) of t:e isolator ' an; measure t:e ;eflection* 26
%n isolator allows signal in onl? one ;irection t:at is from port ) to port 2 an; ;oesnFt allow t:e signal in t:e reverse ;irection t:at is from port 2 to port )*
27
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K!rid"ar #a$u E/periment 96
Date Measurement of !0#
< o measure t:e stan;ing wave Ratio for t:e given loa; at a specifie; freuenc? using ;irect met:o;* (im
E:uipment < 0l?stron power suppl?B @l?stron mount wit: refleA @l?stron oscillatorB IsolatorB
)* 'efore switc:ing on t:e @l?stron power suppl?B t:e repeller voltage @nob s:oul; be put at its maAimum position full cloc@ wise to give maAimum repeller voltage* 2* 0eep t:e beam voltage constant aroun; 399 an; var? t:e repeller voltage to get maAimum ;eflection in S$R meter* Similarl? amplitu;e an; freuenc? of t:e mo;ulating signal :as to be varie; for setting setting maAimum ;eflection* ;eflection* %lso tune t:e probe probe of t:e slotte; section to get maAimum ;eflection*
3* If t:ere is a mismatc: between t:e slotte; section a wave gui;e basicall? wit: a slot an; loa;B stan;ing stan;ing waves will be forme;* forme;* :e stan;ing stan;ing waves can be observe; observe; b? moving t:e t:e probe along along t:e slotte; slotte; section* section* 1* #iA t:e probe at voltage maAimum maA* ;eflection point* $it: t:e :elp of t:e attenuator ma@e t:e ;eflection ;eflection to rea; S$R G )* :at is t:e maAimum maAimum ;eflection is now set to rea; rea; S$R of )*
28
K!rid"ar #a$u
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4* "ow move t:e probe along t:e slotte; section an; fiA t:e probe at voltage minimum point minimum ;eflection* :e rea;ing on t:e S$R scale for t:e voltage minimum point gives S$R of t:e given loa;* 5* Repeat t:e above process process for various various loa;s w:ose S$R value ;oesnQt ;oesnQt eAcee; )9* #or loa;s w:ose S$R eAcee;s )9B we use 3 ;' met:o; Double minimum met:o; for fin;ing stan;ing wave Ratio* 6* Since S$R of a loa; is a function of a freuenc?B we :ave to measure t:e freuenc? of t:e signal b? using cavit? meter* #esults <
)* S$R of (orn antenna G 2* S$R of Matc:e; loa;* G 3* S$R of S:ort Circuit termination G
39
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K!rid"ar #a$u
E/periment 9>
Date C"aracteristics of Circulator
(im<
o ;etermine t:e c:aracteristics of t:e given circulator an; to obtain its Scattering matriA* E:uipment <
0l?str 0l?stron on power power suppl suppl??B @l?str @l?stron on Mount Mount wit: wit: RefleA RefleA 0l?st 0l?stron ron osci oscilla llato torB rB IsolatorB ariable %ttenuatorB Cavit? meterB wave gui;e ;etectorB S$R meterB Matc:e; loa;B circulator* Block diagram of t"e circuit <
.rocedure< )* Connect t:e above circuit wit:out t:e circulatorB t:at is wave gui;e ;etector is
to be connecte; to cavit? meter* 2* %;ust t:e Reflector oltageB %mplitu;e of t:e Mo;ulating signal #reuenc? of t:e Mo;ulating signal to get maAimum ;eflection in t:e S$R meter* "ote ;own t:e rea;ings of 'eam voltage an; Reflector voltage* 3* :e maAimum ;eflection now ma? not be rea;ing 9 ;' wit: t:e :elp of variable %ttenuator %ttenuator ma@e t:e ;eflection ;eflection to rea; 9 ;' on ;' scale scale in t:e S$R meter* :at is t:e maAimum ;eflection is now a;uste; to rea; 9 ;' reference level* 1* "ow insert t:e circulator between cavit? meter an; t:e wave gui;e ;etector as s:own in t:e figure* :at is we are giving giving a signal of 9 ;' reference reference to port ) of t:e circulato circulatorr an; 3)
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measur measuring ing t:e signal signal streng strengt: t: in ;' at port port 2 b? connec connectin tingg a ;etec ;etecto torr wit: wit: port port 3 terminate; in Matc:e; loa;* 4* Inter c:ange t:e port 2 an; 3 i*e* connect t:e ;etector to port 3 an; Matc:e; loa; to port 2 an; measure t:e ;eflection* 5* Repeat t:e above process b? giving t:e signal of 9 ;' reference to port 2 an; 3 an; note ;own t:e rea;ings as s:own below* Observations <
Input Port Port ) Port 2 Port 3
Conclusion <
Input signal G 9 ;' reference* Matc:e; Port !utput Port 3 2 ) 3 ) 2
:ere is coupling from port ) to port 2 from port 2 to 3 an; from port 3 to
port )* ?pical rea;ings< $:en port ) is fe; reference 9 ;' Power measure; at port 2 G K9*4 ;' Power measure; at port 3 G K39 ;'* )9 log S2)2 G K9*4 29 log S2) G K9*4 )9 log S3)2 G K39 29 log S3) G K39
S2) G 9*811 S3) G 9*93)5
$:en port 2 is fe; reference 9 ;' Power measure; at port 3 G K9*4 ;' 32
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Power measure; at port ) G 9*93)5
S 32 G 9*811B S)2 G 9*93)5
$:en port 3 is fe; reference 9 ;' Power measure; at port ) G K9*4 ;' Power measure; at port 2 G K39 ;'
S )3 G 9*811B S23 G 9*93)5
%ssume t:at all t:e ports are matc:e; S )) G S22 G S33 G 9
9 Scattering Scattering MatriA S G 9*811 9*93)5
9*93)5 9*811 9 9*811
33
9*3)5 9
K!rid"ar #a$u
wwwengglabsblogspotcom
31
K!rid"ar #a$u
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34
K!rid"ar #a$u
wwwengglabsblogspotcom
E/periment 9?
Date 2ybrid +EE
(im
< o ;etermine t:e c:aracteristics of t:e given (?bri; ee*
< 0l?str 0l?stron on pow power er suppl? suppl?BB RefleA RefleA @l?str @l?stron on oscil oscillat lator or wit: wit: mo mount unt isola isolator torBB ariable %ttenuatorB #reuenc? meterB wavegui;e ;etectorB (?bri; eeB Matc:e; loa;sB S$R meter* E:uipment
Block diagram of t"e circuit <
.rocedure<
)* Set up t:e microwave benc: as s:own in t:e figure wit:out connecting t:e (?bri; ee ee w:ose c:aracteristic c:aracteristic are to be obtaine;* obtaine;* :at is t:e freuenc? meter s:oul; be followe; b? t:e wavegui;e ;etector an; S$R meters* 2* !perate t:e 0l?stron in I" mo;e 3* 0eep t:e 'eam voltage constant 399 an; var? t:e repeller voltageB freuenc? an; amplitu;es of t:e mo;ulating signal for obtaining maAimum ;eflection in t:e S$R meter* %lso tune t:e probe for maAimum ;eflection*
35
K!rid"ar #a$u
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1* %;ust t:e attenuation b? using t:e variable attenuator an; ma@e t:e ;eflection to rea; 9 ;' in S$R meter* :e signal of 9 ;' reference reference level will be given as t:e input to (?bri; ee* 4* "ow insert t:e (?bri; ee ee as s:own in t:e figure* :e signal of 9 ;' reference is given given as t:e input to port ) Measure t:e power relative power at port 2 b? connecting MJL at port E an; ( similarl? measure t:e powers at ports E an; ( b? connecting MJL at ot:er ports* 5* "ow t:e signal of 9 ;' reference s:oul; be given to port 2 an; measure t:e power at ot:er ports* Repeat t:is process b? giving t:e signal to ports E an; (* #eadings < Input Signal G 9 ;' reference
(im< o measure t:e insertion loss of t:e given attenuator* E:uipment <
0l?str 0l?stron on pow power er suppl suppl??B Refle RefleAA @l?str @l?stron on oscil oscilla lator tor wit: wit: mo mount untBB isola isolator torBB ariable attenuatorB #reuenc? meterB wave gui;e ;etectorB S$R meter an; given attenuator Block diagram of t"e circuit <
+"eory )* %ttenuators are reciprocal ;evices*
2* %ttenuators %ttenuators are categori>e; categori>e; as fiAe; attenuators attenuators an; variable attenuators attenuators base; on t:e fact w:et:er attenuation attenuation is fiAe; or variable* variable* In variable attenuators attenuators t:e variation variation in attenuation is ac:ieve; b? c:anging t:e position of t:e resistive vanes* 3* %ttenuation i*e*B power loss ;uring transmission t:roug: t:e ;evice is represente; in ;'s* 1* %ttenuators are use; to re;uce t:e power level of t:e incoming microwave signal* .rocedure
)* Setup t:e benc: as s:own in t:e figure 2* $it:out $it:out connecting connecting t:e attenuator to be c:aracterise;B c:aracterise;B energi>e t:e source b? appl?ing a beam voltage voltage of 399 an; repeller repeller voltage voltage for mo;e maAimum maAimum con;ition* con;ition* 3* Set t:e @l?stron power suppl? to operate in Internal mo;ulation mo;e* 1* %; %;us ustt t:e am ampli plitu; tu;ee an; freu freuen enc? c? of t:e mo mo;u ;ulat latin ingg signa signall to obtai obtainn ma maAim Aimum um ;eflection in S$R meter* 37
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4* '? a;usting t:e freuenc? meter ;etermine t:e operating freuenc? of t:e signal* 5* %;ust %;ust t:e variable attenuator attenuator suc: t:at t:e ;eflection rea;s 9 ;' in S$R meter* :at is input power of 9 ;' acts as a reference level for measuring t:e powers at t:e ot:er port* 6* "ow connect t:e attenuator w:ic: is reuire; to be c:aracteri>e; c:aracteri>e; at t:e appropriate appropriate peace as s:own in figure* 7* "ote t:e output power in ;' level* 8* Repeat steps 6 an; 7 b? interc:anging input an; output output ports of t:e given attenuator* attenuator* %s an attenuator is a reciprocal ;eviceB t:e rea;ings s:oul; be same as earlier* Observations < 'eam voltage
G Repeller voltage G
'eam current G #reuenc? G
Power in port );'
Power in port 2;'
9 ;' 9 ;'
E/periment 9A
Date
38
K!rid"ar #a$u
wwwengglabsblogspotcom D*#EC+*O%(L CO7.LE#
(im
< o stu;? t:e c:aracteristics of t:e given ;irection coupler*
E:uipment <
0l?str 0l?stron on power power suppl? suppl?BB Refle RefleAA 0l?str 0l?stron on oscill oscillat ator or wit: wit: mo moun untBtB isola isolator torBB ariable attenuatorB #reuenc? meterB ;irectional couplerB wavegui;e ;etectorB S$R meter an; matc:e; loa;* Block diagram of t"e circuit <
+"eory< Directional coupler is a 1 port reciprocal ;evice*
It samples energ? in one ;irection onl?* % two :ole ;irectional coupler consists of a piece of transmission line to be connecte; in series wit: t:e main lineB toget:er wit: a piece of auAiliar? line couple; to t:e main line via two probes t:roug: slots in t:e oine; outer walls of t:e two coaAial lines as s:own in figure*
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P ort 3
P ort 4 (M a tc h e d )
A
B
λ /4
P ort 2
P ort 1
:e probes probes ;o not actuall actuall?? touc: t:e inner inner con;uct con;uctor or of t:e auAiliar? auAiliar? line* line* :e ;istance ;istance between t:e probes probes is J1* J1* :e auAiliar? auAiliar? line is terminate; terminate; at at one en; b? a matc:e; loa;* loa;* If a signal is fe; to port ) Input port it travels along t:e main line an; reac:es port 2 ;irect port* $:en t:e signal travels along t:e main line it is couple; b? t:e probes % an; ' eac: of lengt: QlQ* :e signals couple; couple; b? t:e probes % an; ' travel t:e same ;istance of lHJ1 before before reac:ing port 3* So bot: t:e signals of in p:ase will be a;;e; at port 3* In a )9 ;' ;irectional coupler coupler )J)9 in of t:e input signal reac:es reac:es port 3* Signal available available at port 1 in an i;eal i;eal ;irectional ;irectional coupler coupler s:oul; be >ero >ero because because t:e signals signals couple; b? probes probes % an; ' will :ave a pat: ;ifference of J2 p:ase ;ifference of )79 9 before t:e? reac: port 1 an; :ence t:e get cancelle;*
Coupling coefficient
C G )9 log P )JP3
Directivit?
D G )9 log P 3JP1
Isolation
G )9 log P )JP1
Insertion loss
I L G )9 log P )JP2
1)
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.rocedure<
)* Set t:e microwave benc: as s:own in t:e figure wit:out t:e ;irectional coupler being connecte;* 2* !perate t:e @l?stron oscillator in internal mo;ulation mo;e* 3* 0eep t:e 'eam voltage constant sa? 399 an; a;ust t:e repeller voltageB amplitu;e an; freuenc? of t:e mo;ulating signal to get maAimum ;eflection in S$R meter* 1* "ow wit: t:e :elp of variable attenuator a;ust t:e ;eflection to rea; 9 ;' in S$R meter* :is will be ta@en as a reference level for measuring t:e power at t:e ot:er ports* 4* "ow t:e ;irectional to be c:aracteri>e; c:aracteri>e; s:oul; be inserte; inserte; as s:own in t:e figure* :e signal of 9 ;' reference :as to be given as t:e input to port )* Measure t:e power in ;' at ports 3 an; 2 an; obtain obtain t:e coupling coupling coefficient coefficient an; an; insertion insertion loss* C G )9 log P )JP3 IL G )9 log P )JP2 5* %s port 1 is terminate; terminate; wit: a matc:e;B matc:e;B t:is port is not accessible to measure t:e power at t:at port* %s a ;irectional coupler is a s?mmetrical an; reciprocal ;eviceB fee;ing port ) an; measuring t:e signal at port 1 is euivalent to fee;ing t:e ;irectional coupler at port 2 an; measuring it at port 3* SoB now give give t:e signal signal of 9 ;' reference reference to port 2 an; measure t:e t:e power at port 3 :is is eual eual to P 1 Isolation G )9 log P )JP1 Directivit? G )9 log P 3JP1 ?pical ?pical rea;ings< Signal of 9 ;' level is ta@en as a reference level is applie; to port )
P)
G 9 ;' Power at port 3 G K)9 ;' Power at port 2 G K9*7 ;' "ow give t:e signal of 9 ;' reference reference to port 2 an; measure t:e signal at port 3 :is is eual to giving t:e signal at port ) an; measuring it at port 1* P1 G K1) ;'*
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C G )9 log P)JP3 G )9 ;' IL G )9 log P)JP2 G 9*7 ;' Directivit? D G )9 log P 3JP1 G 3) ;' Isolation I G )9 log P )JP1 G 1) ;' Observations Input Power G 9 ;' reference
$:en Input is given to Port ) Power at Port 2 i*e* P2 G Power at Port 3 i*e* P 3 G $:en Input is given to Port 2 Power at Port 3 i*e* P 1 G
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E/periment 9
Date *mpedance Measurement
< o stu;? t:e met:o; of measuring un@nown loa; impe;ance b? measuring S$R an; t:e position of voltage minimum*
(im
< 0l?stro 0l?stronn power power suppl? suppl?BB RefleA RefleA @l?stro @l?stronn oscillat oscillator or wit: mountB isolator isolatorBB variable attenuatorB #reuenc? meterB slotte; section wit: movable probeB S$R meterB S:ort circuitB loa; w:ose impe;ance is to be measure;*
E:uipment
Block Diagram of t"e Circuit <
:e microwave energ? inci;ent on t:e loa; from t:e generator is reflecte; if t:e loa; is not eual to t:e c:aracteristic c:aracteristic impe;ance* impe;ance* :e amount of reflecte; reflecte; energ? an; :ence t:e value of S$RB t:e relative position of t:e voltage minimum are ;epen;ent on t:e c:aracteristics of t:e loa;*
+"eory
:e input impe;ance of a transmission line can be written as in G s J Is G R Cos: Ul H IR o Sin: Ul IR Cos: Ul H R Jo Sin: Ul #or a loss less line U G VHW re;uces to W R H 9 tan Wl in G 9 9H R tan Wl 11
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$:en rearrange; for R inK o tan Wl R G
9 oK in tan Wl
R Jo G
)KoJin tan Wl oJin Ktan Wl
R Jo G )K S tan Wl
$:ere SGoJin G S$R of t:e loa;*
S K tan Wl "ormali>e; loa; loa; impe;ance impe;ance ) K S tan 2X lJg r G R J9 G S K tan 2X lJg
.rocedure< )* %rrange t:e set up as s:own in figure*
2* !perate t:e 0l?stron oscillator in I" mo;ulation mo;e* 3* Connect s:ort circuit as t:e loa;* 1* 0eep t:e 'eam voltage constant 399 an; a;ust t:e repeller voltageB freuenc? an; amplitu;es of t:e mo;ulating signal for obtaining maAimum ;eflection in S$R meter* 4* 'ecause of t:e mismatc: between t:e loa; s:ort circuit an; t:e wave gui;e slotte; sectionB stan;ing wave will be forme; along t:e lengt: of t:e slotte; section w:ic: can be observe; b? moving t:e probe t:e slotte; section* 5* "ote ;own t:e probe position correspon;ing to voltage minimum points* :e ;istance between two successive successive minimum points is eual to gJ2 from w:ic: gui;e wavelengt: g can be obtain*
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H orn
s/c Towards G e n e t a t o r d s
d L4 5
d L 3 d s
d s
4
d L1
dL2 3
ds2
d s
1
λ g 2
;s1K;s3 G gJ2
g G 2;s1K;s3
6* "ow replace t:e s:ort circuit wit: t:e loa; w:ose impe;ance :as to be obtaine;* Stan;ing waves are forme; once againB can be observe; b? moving t:e probe along t:e slotte; section* section* "ote ;own t:e probe position position correspon; correspon;ing ing to voltage voltage minimum minimum points* points* -ou can observe t:at t:e stan;ing wave pattern is s:ifte; compare; to t:e one w:ic: is obtaine; for SJC loa;* g G 2;L1K;L3 l G ;S4K;L1 G ;S1K;L3 #or obtaining s:ift in minimum alwa?s start at a SJC minimum point an; move towar;s t:e loa; en; till a loa; minimum in obtaine;* obtaine;* :e ;ifference ;ifference is s:ift in minimum* minimum* "ote t:at ;L1K;S1 an; ;L3K;S3 will note be eual to s:ift in minimum* 7* "ow move t:e probe along t:e slotte; section an; fiA t:e probe at voltage maAimum point w:ic: can be observe; in S$R meter* $it: $it: t:e :elp of variable attenuator attenuator a;ust t:e ;eflec ;eflectio tionn to rea; S$RG) S$RG) on t:e S$R scale scale of S$R S$R me meter ter** :at :at is t:e t:e ma maAim Aimum um ;eflection correspon;s to voltage maAimum points :as been a;uste; to rea; S$R G ) "ow move t:e probe along t:e slotte; section an; fiA t:e probe at voltage voltage minimum point* :e rea;ing on S$R scale for t:is minimum ;eflection is not:ing but t:e S$R of t:e loa;* 8* %lso measure t:e freuenc? of t:e signal wit: t:e :elp of freuenc? meter*
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wwwengglabsblogspotcom 'eam voltage G 'eam current G #reuenc? of t:e signal G S$R of t:e loa; (orn antenna S G S:ift in minimum YlZ G .ui;e wave lengt: g G
Observations
) K S tan 2X lJg "ormali>e; "ormali>e; loa; impe;ance impe;ance R Jo Gr G R J9 G
SKtan2XlJ g
9 is t:e c:aracteristic impe;ance of t:e wave gui;e* L!
=
366 2
λ ) K λ C
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E/periment 93
Date (ntenna 8ain Measurements
(im< o measure t:e gain of a wave gui;e :orn* E:uipment <
) ) ) ) ) ) ) ) ) ) )
0l?stron power suppl? 0l?stron mount wit: @l?stron tube Isolator ariable attenuator #reuenc? meter Stan;ing wave ;etector Slotte; wavegui;e section ariable s:ort S$R meter ermination (orn %ntenna
+"eory <
.ain< . G :e power intensit? at t:e maAimum of t:e main lobe compare; to t:e power intensit? ac:ieve; from an imaginar? omni ;irectional antenna ra;iating euall? in all ;irectionsB wit: t:e same power fe; to t:e %ntenna* $:en measuring an %ntenna pattern it is normall? most interesting to plot t:e pattern far from t:e %ntenna t:e pattern close to t:e antenna loo@s ;ifferent* ;ifferent* % far fiel; pattern is ac:ieve; ac:ieve; at a minimum ;istance ;istance of R min* R min G 2D2Jo rectangular :orn antenna $:ere D G :e si>e of t:e broa;er wall of t:e :orn aperture* o G :e free space wave lengt:
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It is also ver? importa important nt to avoi; avoi; ;isturbing ;isturbing reflecti reflections* ons* %n %ntenn tennaa measure measuremen ments ts are normall? ma;e at out;oor ranges or in so calle; anec:oic c:ambers ma;e of absorbing material* %ntenna measurements are mostl? ma;e wit: t:e un@nown antenna as receiver* :ere are several several met:o;s met:o;s to measure measure t:e gain of an antenna* antenna* !ne met:o; met:o; is to com compare pare t:e un@nown un@nown antenna wit: a [Stan;ar; gain[ antenna wit: well @nown gain* %not:er met:o; is use; two i;entical antennasB one as transmitter an; t:e ot:er an receiver* :e following formula can be prove; s?mbols in #ig*)* 2
Pr
=
:us
2
Pt . λ 9
( 1 π R )
9 G free space wavelengt:
2
.
= 1 Π R λ 9
Pr Pt
PtB Pr an; an; R are measure; an; . can be calculate;* %s can be seen from t:e formula it is not necessar? to @now t:e absolute values of P t an; Pr B onl? t:e ratio* ratio* :is can can be measure; measure; wit: a suare low ;etector matc:e;* Block Diagram of t"e Circuit <
4)
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.rocedure<
)* 2* 3* 1*
Set Set up up t:e t:e eui euipm pmen entt as as ss:o :own wn in #igu #igure re** Ener Energi gi>e >e t:e t:e 0l? 0l?st stro ronn b? conn connec ecti ting ng ter termi mina nati tion on** %;us %; ustt t:e t:e repe repelle llerr volta voltage ge to to get get maAim maAimum um ;efle ;eflect ction ion on on t:e t:e S$R S$R mete meter* r* Set t:e t:e range range swit switc: c: on 39 39 ;' 19 ;' ;' posit position ion a;ust a;ust pro probe be pene penetra tratio tionn to obta obtain in up scale rea;ing* 4* %; %;us ustt t:e mo;ul mo;ulati ation on freu freuen enc? c? of t:e t:e signa signall source source to to get maAim maAimum um ;efle ;eflect ction ion an; an; also tune t:e probe ;etector* 5* %; %;us ustt gain gain contro controls ls for for output output powe powerr from from t:e sign signal al sourc sourcee to obtain obtain eAa eAact ctl? l? fullK fullK scale rea;ing* 6* '? conne connectin ctingg t:e t:e termin terminatio ationn after after t:e slotte; slotte; sectionB sectionB measure measure t:e power power level level P t* 7* Remo Remove ve t:e t:e term termin inat atio ionn an; con conne nect ct (orn (orn ant anten enna na** %t a ;ista ;istanc ncee of )*4 )*4 mB plac placee (orn antenna receiver at t:e same :eig:t as t:at of ransmitting (orn antenna* 8* Conne Connect ct t:e t:e termi terminal nal on on to t:e t:e (orn (orn ant anten enna na RA RA an; an; mea measur suree t:e powe powerr leve levell P r * 8* Measure g* )9* .ain of t:e antenna can be obtaine; obtaine; using t:e Euation* Euation* Observations
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E/periment 933
Date C"aracteristics of 8unn Oscillator
(im<
o stu;? t:e following c:aracteristic of .unn Dio;e* )* KI C:aracteristic 2* !utp !u tput ut powe powerr an; an; fre freue uenc nc?? as as a fun funct ctio ionn of of vol volta tage ge** 3* Su Suare are wa wave mo;ul ;ulation tion t:rou roug: PI PI" ;i ;io;e* E:uipment <
.unn oscillatorB .un power suppl?B Pin Mo;ulatorB Isolator #reuenc? MeterB ariable %ttenuatorB Detector MountB $avegui;e Stan;sB MeterB Cables an; accessories* +"eory < :e .unn oscillator is base; on negative ;ifferential con;uctivit? effect in bul@ semicon;uctors w:ic: :as two con;uctions ban;s separate; b? an energ? gap greater t:an t:ermal agitation agitation energies* energies* % ;isturban ;isturbance ce at t:e cat:o;e gives rise to :ig: region w:ic: travels towar;s t:e ano;e* $:en t:is :ig: fiel; ;omain reac:es t:e ano;eB it ;isappears an; anot:er ;omain ;omain is forme; at cat:o;e an; starts starts moving towar;s towar;s ano;e an; so on* :e time reuire; for ;omain to travel from cat:o;e to ano;e transit time oscillation freuenc?* In a .unn oscillatorB oscillatorB t:e .unn ;io;e is place; in a resonant cavit?* cavit?* In t:is case t:e freuenc? is ;etermine; ;etermine; b? cavit? ;imension ;imension t:an b? ;io;e ;io;e itself* %lt:oug: %lt:oug: .unn can be amplitu;eKmo;ulate; wit: t:e voltage* $e :ave use; separate PI" mo;ulator t:roug: PI" ;io;e in suare wave mo;ulation* % measure of t:e suare wave mo;ulation capabilit? is t:e mo;ulation ;ept: i*e* t:e output ratio between Q!"Q an; Q!##Q state* Block Diagram of t"e Circuit <
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1 * c"aracteristics of 8unn Oscillator Oscillator
current (mA)
Thresho!d o!tage
o!tage(o!ts)
.rocedure<
Set t:e components an; euipment as s:own in t:e figure initiall? set t:e variable attenuator for maAimum attenuation* 0eep t:e control @nob of .unn Power Suppl? as below < Meter Switc: .unn bias @nob Pin bias @nob Pin Mo; freuenc?
K K K K
Q!##Q #ull? anticloc@wise #ull? antiKcloc@wise %n? position
0eep t:e control @nob of S$R meter as below< Meter Switc: Input Switc: Range ;b Switc: .ain Control @nob
K K K K
Q"ormalQ Low Impe;ance 19 ;' #ull? cloc@wise
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Set t:e microme micrometer ter of .unn oscillat oscillator or for reuire; reuire; freuen freuenc? c? of operatio operation* n* Q!"Q t:e .unn Power suppl?B S$R Meter an; Cooling #an* (
1oltag tage 9 Current C" C"aracter teristic stic
)* 2*
urn urn t:e t:e mete meterr switc: switc: of .un .unnn power power suppl suppl?? to volt voltag agee posit position ion** Measur Measuree t:e .unn .unn ;io; ;io;ee current current corre correspo spon;i n;ing ng to t:e t:e variou variouss voltag voltages es contro controlle lle;; b? .unn bias @nob t:oug: t:oug: t:e panel panel meter an; meter meter witc:* Do not t:e eAcee; eAcee; t:e bias voltage above )9 volts* Plot Plot t:e t:e volt voltage age an; an; curre current nt rea rea;in ;ings gs on on t:e t:e grap grap:: as s:own s:own in in figu figure* re* Measur Measuree t:e t:e t:res t:res:o :ol; l; volt voltage age w:ic: w:ic: corr corres espon pon;s ;s to to maAim maAimum um curre current* nt*
Outt p Ou put ut .owe .owerr and and ,re: ,re:ue uenc ncy y as as a ,un ,unct ctio ion n of of Bia Biass 1o 1oltag ltagee <
urn urn t:e t:e meter meter wit witc: c: of of .unn .unn powe powerr supp suppl? l? to to volt voltage age positi position* on* Incr Increa ease se t:e t:e .un .unnn bia biass con contr trol ol @nob @nob** Rota Rotate te PI" PI" bia biass @nob @nob to to aro aroun un;; maA maAim imum um pos posit itio ion* n* une une t:e output output in t:e t:e S$R meter meter t:roug t:roug:: freu freuenc? enc? control control @nob of mo;u mo;ulati lation* on* If nece necess ssar ar?? c:ang c:angee t:e t:e rang rangee ;' swit switc: c: of S$R S$R mete meterr to :ig: :ig:er er or lowe lowerr ;' position position to get ;eflection ;eflection on S$R meter* meter* %n? level can be set t:roug: variable attenuator an; gain control @nob of S$R meter* Measur Measuree t:e t:e freu freuenc enc?? b? b? fre freu uenc enc?? mete meterr an; an; ;etu ;etune ne it* it* Re;u Re;uce ce t:e t:e .u .unn nn bias bias volt voltag agee in t:e t:e inte interv rval al of 9*4 9*4 or )*9 )*9 an; an; note note ;own ;own correspon;ing rea;ing of output at S$R meter an; freuenc? b? freuenc? meter* +se t:e t:e rea;i rea;ing ng to ;rawn ;rawn t:e t:e Power Power vs vs o oltage ltage curv curvee an; fre freue uenc? nc? vs vs volta voltage ge an; an; plot t:e grap:* grap:* Meas Measur uree t:e t:e pus: pus:in ingg fact factor or in in M(>* M(>* olt lt w: w:ic ic:: is freu freuen enc? c? sensi sensiti tivi vit? t? agai agains nstt variation in bias voltage* :e pus:ing factor s:oul; be measure; aroun; 7 volt bias*
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C
)* 2* 3* 1* 4*
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!:uare 0ave Modulation <
0eep 0eep t:e t:e meter meter switc switc:: of .unn .unn Power Power Supp Suppl? l? to vol voltt positi position on an; an; rotat rotatee .unn .unn bias bias voltage slowl? so t:at panel meter of .unn Power Suppl? rea;s )9 * une une t:e t:e PI" mo;u mo;ulat lator or bias bias volt voltage age an; an; fre freuen uenc? c? @nob @nob for for maAim maAimum um outpu outputt on t:e oscilloscope* Coinci;e Coinci;e t:e botto bottom m of suare suare wave wave in !scil !scillosc loscope opess to some some referen reference ce level level an; note note ;own t:e micrometer rea;ing of variable attenuator* "ow "o w wit: wit: :elp :elp of vari variab able le atte attenu nuat ator or coinc coinci; i;ee t:e t:e top top of sua suare re wave wave to same same reference level an; note ;own t:e micrometer rea;ing* Conn Connec ectt S$ S$R R to ;ete ;etect ctor or mou mount nt an; an; not notee ;own ;own t:e t:e ;'* ;'*
Observations
'ias oltage
Current m%
#reuenc?
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E/periment 93;
Date Measurement of #adiation .attern of 2orn (ntenna
(im<
o measure t:e Ra;iation Pattern of t:e given :orn antenna*
E:uipment <
) ) ) ) ) ) ) 2
0l?stron power suppl? 0l?stron mount wit: @l?stron tube Isolator ariable attenuator #reuenc? meter wave gui;e ;etector S$R meter (orn %ntennas
+"eory <
$:en measuring an %ntenna patternB it is normall? most interesting to plot t:e pattern far from t:e %ntenna %ntenna t:e pattern close to t:e antenna loo@s ;ifferent* ;ifferent* % far fiel; pattern is ac:ieve; ac:ieve; at a minimum ;istance ;istance of R min* R min G 2D2Jo rectangular :orn antenna $:ere D G :e si>e of t:e broa;er wall of t:e :orn aperture* o G :e :e fre freee spac spacee wav wavee leng lengt: t: It is also ver? importa important nt to avoi; avoi; ;isturbing ;isturbing reflecti reflections* ons* %n %ntenn tennaa measure measuremen ments ts are normall? ma;e at out ;oor ranges or in so calle; anec:oic c:ambers ma;e of absorbing material* %ntenna measurements are mostl? ma;e wit: t:e un@nown antenna as receiver* :e Electric fiel; strengt: of an antennaB in general is a function of t:e angles Q\Q an; ]F* If one woul; li@e to reprsent t:e variation of Electric fiel; intensit? interms of t:ese anglesB we reuire a t:ree ;imensional grap:* :e same can be represente; b? using 2B two ;imensional grap:s* ariation of Electric fiel; wit: \B @eeping ] constant is @nown as :ori>ontal pattern* ariation of Electric fiel; wit: ] B @eeping \ constant constant is @nown as vertical pattern* In power pattern we s:ow t:e variation of power receive; in terms of t:e angles \ an; ] ^Ra;iation Ra;iation 47
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pattern is a general term w:ic: ;efines eit:er t:e fiel; pattern or t:e power pattern* pattern* In general t:e antenna for w:ic: t:e ra;iation pattern is to be foun;B is use; as t:e receiving antenna* $e can use an? ot:er antenna as t:e transmitting antenna ;esigne; for t:e same freuenc? of operation* In t:is two (orn antennas are use;B one as transmitting an; t:e ot:er as t:e receiving antenna* Block Diagram of t"e E/perimental setup <
.rocedure<
)* Set up up t:e t:e euipm euipment ent as as s:own s:own in t:e t:e #igure #igure** 2* Energise Energise t:e 0l?stron b? connecting connecting (orn antenna as transmitting transmitting antenna* antenna* 3* +se %not:er %not:er :orn antenna antenna as t:e receivi receiving ng antenna* antenna* 'ot: t:e antennas antennas s:oul; s:oul; be of t:e same :eig:t from t:e groun;* 1* 0eep t:e beam voltage constant constant aroun; 399 volts* %;ust t:e repeller voltage to get get maAimum ;eflection in t:e S$R meter* 4* Set t:e t:e range range switc switc:: in 39 39 ;' or or 19 ;' ;' positio position* n* 5* %;ust t:e t:e mo;ulating mo;ulating signal signal freuenc? freuenc? an; an; its amplitu;e amplitu;e to to get maAimum maAimum ;eflection ;eflection in S$R meter* meter* "ow t:e benc: is set to eAtract maAimum power from t:e @l?stron oscillator* 6* "orma "ormall? ll? w:en t:e trans transmi mitti tting ng an; an; t:e t:e recei receivin vingg anten antennas nas loo@ at eac: eac: ot:e ot:erB rB maAimum maAimum ;eflectio ;eflectionn can be observe; observe; in t:e output output meter* meter* %; %;ust ust t:e variable variable attenuator an; set t:e maAimum ;eflection to rea; 9 ;'* :is can be ta@en as t:e reference level for measuring power in ;'* 7* $:en $:en bot: bot: ante antenn nnas as loo@ loo@ at eac: eac: ot:e ot:erB rB t:e posit positio ionn is ta@en ta@en as \G9 \G9 ]G9* ]G9* %s %s mentione; earlierB maAimum ;eflection can be observe; in S$R meter in t:is position w:ic: w:ic: is set to to rea; 9 ;'*
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8* "ow move t:e recei receivin vingg ante antenna nna aroun; aroun; t:e t:e transm transmitt itting ing antenn antennaa in :ori> :ori>on ontal tal ;irection ;irection for getting getting :ori>ontal :ori>ontal ra;iation ra;iation pattern* pattern* Rotate t:e receiving receiving antenna in cloc@ wise ;irection ;irection in steps of )9 9 an; note ;own t:e ;eflection in t:e S$R meter me ter till till \ G89 G899* "ow move t:e antenna in anti cloc@ wise ;irection up to \G K 899* :is results in :ori>ontal ra;iation pattern w:en it is plotte;* )9* Similarl? w:en t:e receiving receiving antenna is move; in t:e up an; ;own war; ;irections ;irections i*e* c:anging c:anging t:e value value of ]B_ @eeping @eeping \ constantB constantB results in vertical pattern* $:en vertical pattern pattern is measure;B measure;B t:e receiving receiving antenna s:oul; not be move; eit:er to t:e left or to t:e rig:t as it c:anges t:e value of \ T y p i c a l R a d i a t io io n p a t t e r n
Measurement of #adiation .attern of 4 Element )agi 7da (ntenna
(im o stu;? t:e ra;iation pattern of 3 element -agi +;a antenna* (pparatus %ntenna trainer @it along wit: various antennas
:eor?< In t:isB t:e oltage Stan;ing $ave Ratio S$R an; t:e ra;iation c:aracteristics of various antennas will be measure; an; a comparison can be ma;e* #or an antenna to be effective as a ra;iatorB it :as to be properl? matc:e;* :e amount of mismatc: can be foun; b? measuring t:e S$R of t:e antenna* $:enever t:ere is a mismatc: between t:e line an; t:e loa;B stan;ing stan;ing waves are forme;* S$R is ;efine; as t:e ratio of voltage maAimum to voltage minimum* S$R G oltage maAimumJ oltage minimum :e S$R value is relate; to t:e Reflection coefficient in t:e following manner* S$R G
If Pi represents t:e Inci;ent Power 2 0 P represents t:e amount of Reflecte; Power an; t:e remaining represents t:e forwar; power i
t:at :as been transferre; to t:e loa;* :e ot:er important c:aracteristic of an antenna is its ra;iation pattern* It gives ?ou an i;ea about t:e ;irection along w:ic: it ra;iates maAimum an; t:e ;irections in w:ic: t:e ra;iation is minimum* :e ra;iation pattern of an antenna can be measure; as eAplaine; in t:e previous eAperiment*
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29* (enceB t:e ra;iation pattern is similar to figure of Ra;iation Pattern Observations
2)* Polar c:art of #ol;e; Dipole %ntenna* 22* In t:e same met:o; as eAplaine; above ?ou ma? ;raw t:e ra;iation pattern forB ot:er ;ipoles p:ase arra?sB slot antennaB loop antenna etc* "* '< %ll %ll t:e rea;ings rea;ings note; are are measure; measure; an; are li@el? li@el? to c:ange c:ange if an?bo;? an?bo;? stan;s stan;s close b? to RA or A antennas antennas or an? metallic metallic obect close b? is situate;* situate;*
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)* Define Define Cut Cut off off wave wave leng lengt: t: of a wave wave gui;e gui;e 2* $:at $:at ;o ?ou ?ou mean b? b? a ;ominan ;ominantt mo;e mo;e in a wave wave gui;e gui;e 3* % wave wave gui; gui;ee acts as as a (ig: pass pass filte filterK rK `ustif? `ustif? 1* Defi Define ne EM EM mo; mo;ee 4* $:at are t:e t:e ;ifferenc ;ifferences es between between transmissio transmissionn lines lines an; wave gui;es gui;es 5* $:? t:e t:e transmis transmission sion lines lines are not not preferre; preferre; at :ig: :ig: freuen freuencies cies** 6* $:at $:at are t:e vario various us t?pes t?pes of wave wave gui;es gui;es use; use; commonl? commonl?** 7* % parallel parallel plate plate wave gui;e gui;e :as a cut off off freuenc? freuenc? of 7 .(>* .(>* % signal of freuenc? freuenc? 5 .(>* is applie; to t:e wave gui;e* Does it propagate 8* $:at $:at is a stan; stan;ing ing wave wave pattern pattern +n;er w:at w:at con;it con;ition ionss it is forme; forme; in a wave wave gui;e* )9* $:at is t:e ;istance between between two minimum points in a stan;ing wave pattern pattern ))* $:at is t:e relations:ip relations:ip between Reflection Reflection coefficient coefficient an; S$R )2* % wave gui;e is termina terminate; te; in a Resistiv Resistivee loa;* loa;* If t:e reflect reflection ion coeffici coefficient ent is 9*2B $:at is t:e S$R of t:e loa; )3* In a stan;ing stan;ing wave pattern pattern if t:e voltage voltage maAimum maAimum is )*2 an; t:e voltage voltage minimum is 9*4B w:at is t:e S$R of t:e loa; )1* :e gui;e wave lengt: in a wave gui;e is alwa?s alwa?s KKKKKK t:an free space wave lengt: )4* :e range of S$R is is KKKKKK )5* :e range of Reflection Reflection coefficient coefficient is KKKKKKK KKKKKKK )6* In M mo;e minimum value of %ttenuatio %ttenuationn is obtaine; at a freuenc? KKKK times t:e cut off freuenc? in a parallel plate wave gui;e* )7* Substitu Substituting ting mG9 in M euations euations results results in EM mo;e* in a parallel parallel plate plate wave ,(L!E gui;e +#7E5 ,(L!E
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)8* In pass pass ban; ban;BB t:e propa propaga gatio tionn const constant ant in a paral parallel lel plate plate wave wave gui;e gui;e beco becomes mes completel? imaginar? 29* :e c:aracteristic c:aracteristic wave impe;ance impe;ance of a wave wave gui;e operating operating in M mo;e mo;e is KKKKKKKK t:an t:e free space impe;ance 2)* $:at are limitations limitations of a circular wave gui;e compare; compare; to a rectangular wave gui;e* gui;e* 22* !f t:e following mo;es mo;es w:ic: is t:e ;ominant mo;e in a circular wave gui;e a* E)) b* E)9 c* M)) ;* M)9 23* Mention t:e freuenc? freuenc? ban; at w:ic: t:e Microwave Microwave Lab is con;ucte;* 21* $:at is t:e material material use; in Circulators Circulators an; Isolators* Isolators* 24* $:at is #ara;a? rotation rotation 25* $:at is t:e Cut off wave wave lengt: of $RK89 $RK89 wave gui;e 26* $:at is t:e relations:ip between t:e reflection reflection coefficient coefficient an; t:e loa; impe;ance 27* $:at is t:e reflection reflection coefficient coefficient of a pure capacitive loa; 28* $:at is t:e value of of intrinsic impe;ance impe;ance of free space space 39* $:at is t:e velocit? velocit? of of EM wave 3)* In Smit: c:art one complete complete rotation is eual to :ow man? wave lengt:s 32* $:at $:at is a g?rator g?rator 33* "ame some of t:e application applicationss of Magic ee ee 31* #or w:at purpose a Directional Directional coupler is use;* EAplain EAplain its wor@ing principle 34* In RefleA 0l?stron !scillator !scillator w:ic: mo;e ?iel;s ?iel;s maAimum out put power 35* $:at is t:e mo;ulation mo;ulation freuenc? in t:e RefleA 0l?stron 0l?stron oscillator oscillator use; in t:e lab 36* $:ic: signal is use; as t:e mo;ulating mo;ulating signal to mo;ulate mo;ulate t:e @l?stron out put 37* $:at is t:e C:aracteristic C:aracteristic impe;ance of Rectangular Rectangular wave gui;e in ;ominant mo;e for a wave of 8 .(>* freuenc?
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38* .ive Scattering Scattering matriA for a loss less less circulator circulator 19* $:? ;o we prefe preferr to use use Scatte Scatteri ring ng matriA matriA at micro microwav wavee freue freuenc ncie iess t:an t:an t:e t:e conventional an; - matrices 1)* $:at is ;ominant ;ominant mo;e in Rectangular Rectangular cavities cavities 12* !n a con;ucting con;ucting surface surface E tan G 9 an; ( normal G 9* rue or #alse 13* (ow ;oes an attenuator attenuator ;iffer ;iffer from an isolator isolator 11* $:? t:e s:ape of t:e material material use; in matc:e; loa; is s:arp an; pointe; pointe; 14* Mec:anical Mec:anical tuning in RefleA @l?stron @l?stron oscillator is ;one b? KKKKKKKKK KKKKKKKKK 15* (ow ;o ?ou c:ange t:e cut off off freuenc? of a Rectangular Rectangular wave gui;e gui;e operating in ;ominant mo;e wit: out c:anging its ;imensions 16* EAplain EAplain t:e importanc importancee of t:e ransit ransit time G n H 3J1 c?cles c?cles in a RefleA @l?stron @l?stron oscillator* 17* Diffe Differe renti ntiate ate betwe between en Elect Electron ronic ic an; an; Mec:a Mec:anic nical al tunin tunings gs in a RefleA RefleA @l?str @l?stron on oscillator* 18* $:? t:e slit is ma;e eAactl? eAactl? at t:e center center of t:e broa;er wall of t:e wave wave gui;e in a slotte; section 49* % c:ange c:ange in repeller voltage c:anges t:e freuenc? freuenc? of oscillations * EAplain 4)* % c:ange c:ange in repel repeller ler volta voltage ge c:an c:anges ges t:e out out put put power power of a RefleA RefleA @l?stro @l?stronn oscillator* EAplain 42* $:? s:oul; s:oul; we mo;ulate mo;ulate t:e signal signal in a RefleA RefleA @l?stron @l?stron oscillator oscillator w:en S$R meter is use; as t:e out put meter 43* $:at is t:e role of an isolator isolator in t:e microwave microwave benc: 41* (ow ;o ?ou ?ou me measu asure re t:e t:e freu freuen enc? c? of t:e microwa microwave ve signal signal generat generate; e; b? t:e t:e @l?stron oscillator EAplain :ow t:e freuenc? meter wor@s 44* $:at is a cr?stal cr?stal ;io;e an; w:? is it calle; calle; as Suare law ;evice ;evice 45* .ive t:e values of reflection reflection coefficient coefficient an; S$R for t:e following loa;s loa;s a* s:ort circuit b* !pen circuit c* Matc:e; loa; ;* pure reactive loa;
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46* #or a certain loa; t:e reflection reflection coefficient coefficient is foun; to be 9*3* $:at is t:e percentage percentage power t:at t:at reflects bac@* bac@* 47* Dimensio Dimensions ns of a rectang rectangular ular wave gui;e ;esigne; ;esigne; for QCQ ban; ban; will be KKKKKKKK KKKKKKKK t:an t:e one ;esigne; for Q/Q ban; freuencies* 48* In observing observing t:e stan;ing stan;ing wave pattern one prefers prefers to note note ;own t:e probe probe position correspon;ing to t:e voltage minimum points compare; to t:e voltage maAimum points* .ive reason for t:at* 59* $:at are t:e i;eal c:aracteristics of (?bri; ee ee $:? is it calle; (?bri; ee ee +n;er w:at con;itions it is calle; as magic ee* 5)* $:at are t:e i;eal i;eal c:aracteristics c:aracteristics of a circulator circulator 52* $:at $:at is t:e t:e ;iffe ;ifferen rence ce betwee betweenn %b %bso sorpt rption ion t?pe t?pe an; an; ran ransmi smissi ssion on t?pe t?pe cavit cavit?? meters* 53* S:oul; t:e gui;e wave lengt: lengt: be more t:an t:e free space wave lengt: lengt: EAplain 51* 51* 'etween t:e cut off wave wave lengt: an; free space space wave lengt: w:ic: :as a :ig:er :ig:er value in or;er to :ave propagation of t:e signal 54* Does t:e .ui;e wave wave lengt: c:ange c:ange wit: t:e loa; EAplain* EAplain* 55* $:at are t:e limitations limitations of conventional conventional tubes at microwave freuencies freuencies 56* (ow t:e Repeller an; %no;e voltages voltages effect t:e ransit ransit time 57* (ow ;o ?ou @eep t:e Repeller Repeller voltage an; 'eam voltage voltage 0nobs before ?ou ?ou switc: on t:e @l?stron power suppl? 58* $:at is meant meant b? a reciprocal reciprocal ;evice* ;evice* 69* :e ;iagonal elements elements of a scattering matriA represent represent KKKKKKKKKKK KKKKKKKKKKK 6)* $:ile $:ile measu measurin ringg t:e t:e Ra;ia Ra;iatio tionn patte pattern rn w:at w:at s:oul; s:oul; be t:e t:e minim minimum um ;istan ;istance ce between t:e t:e transmitting transmitting an; receiving receiving antennas antennas 62* Distinguis: Distinguis: between t:e near fiel; an; t:e far fiel; patterns patterns 63* EAplain about about t:e .unn ;omains ;omains an; t:eir formation formation 61* $:ic: semicon;ucto semicon;uctorr material is use; in .unn .unn ;io;e
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64* Define Define t:e terms terms .ainB .ainB Directi Directivit? vit?BB 'eam wi;t:B wi;t:B 'an; wi;t: wi;t: wit: respect respect to an antenna* 65* EAplain about about t:e properties properties of a scattering scattering matriA 66* EAplain :ow electron electron bunc:es are forme; forme; in a RefleA @l?stron oscillator oscillator 67* In a microwave oven t:e source source of microwave oscillations oscillations is KKKKKKKKKKKK 68* Compare wave gui;esB gui;esB strip lines lines an; micro strip lines lines 79* $:? ;o we prefer prefer to operate t:e wave gui;e gui;e in ;ominant ;ominant mo;e
