ATTENUATION OF MICROWAVE SIGNAL AND ITS IMPACTS ON.docx

Department of Electrical Engineering College of Engineering University of North Texas ATTENUATION OF MICROWAVE SIGNAL AND ITS IMPACTS ON COMMUNICATION SYSTEM By:: By Sanjaya Gurung  ingshu !hao "BST#"CT "Attenuation of Microwave Signal and its Impacts on communication system" is a paper presente$ to ma%e light on the general meaning of attenuation& its impact on communication system an$ the solutions to various %in$s of  attenuation of micro'ave signal( )n this paper& various real 'orl$ examples are illustrate$ 'ith clear *gures an$ graphs to +etter un$erstan$ the characteristics of micro'ave signal propagating in a me$ium( ,arious causes of  attenuation such as rain attenuation& attenuation $ue to trees& long $istance attenuation& other climatic factors such as sno'& 'in$& fog etc( are also $iscusse$ 'ith their solutions( -any technical speci*cations relate$ to ra$io signal propagation an$ attenuation incurre$ is $iscusse$ in this paper( "lmost all relate$ materials are inclu$e$ relevant to attenuation of micro'ave signal an$ its impacts on communication system in this paper

1. Introduction:  Attenuation is the re$uction of signal strength $uring transmission( transmission( )t is just the opposite of amplication( amplication( )ts unit is $B .$eci+el/ or more generally it is measure$ measure$ in $B0%m( $uring the transmission& the signal gets attenuate$ exponentially( "ttenuation is an inherent characteristic of #1 .ra$io fre2uency/ signal an$ also is very important in the $esign aspect( So it shoul$ +e ta%en into consi$eration 'hile $esigning an$ calculating the #S3 .#eceive Signal 3evel/ of the #1 signal +et'een t'o stations( "ttenuation is $irectly proportional to the fre2uency( That means the #1 signal gets signi*cantly signi*cantly attenuate$ at higher fre2uencies an$ there is less e4ect of attenuation at lo'er fre2uencies( 'here& 5 attenuation 5 fre2uency  Transmitter  Transmitter #eceiver #eceiver  Tx antenna #x #x antenna 1ig( +loc% $iagram of a typical communication system me$ium 67'ave )1 ca+le )1 ca+le ,oice0$ata ,oice0$ata )nput signal 8utput signal Electrical signal Electrical signal Electromagnetic 'ave signal

8f course& there is some loss .signal attenuation/ in transmitter as 'ell as in receiver +loc%& ho'ever the major attenuation occurs in the transmission me$ium +et'een Tx an$ #x antennas of t'o stations(

 Attenuation Vs link distance

9

9 1ig( "ttenuation ,s $istance

"ttenuation  The ra$io signal gets attenuate$ exponentially 'hile propagating( 1rom a+ove *gure it is clear that %eeping transmission $istance .$/ *xe$& the higher fre2uency signal .f/ gets attenuate$ signi*cantly than $oes the lo'er fre2uency .f;/ signal( )t is also o+serve$ that 'hen the transmission $istance is near& then the selection of fre2uency .micro'ave antenna of certain fre2uency/ is not so important +ecause there is not much $i4erence.";/ +et'een the attenuation occurre$ +y higher fre2uency an$ lo'er fre2uency 'hereas it is very much important to choose the appropriate fre2uency .micro'ave antenna/ 'hen the transmission $istance is far +ecause there is a signi*cant $i4erence."/ +et'een the attenuation occurre$ $ue to higher an$ lo'er fre2uencies( 8ne shoul$ choose the lo'er fre2uency micro'ave antenna to esta+lish the lin% +et'een the t'o stations locate$ 2uite far a'ay from each other(

Radio Frequency Allocation a!le

Fr!unc" W#$%n&t' R#dio (#nd <=7<== >? ;=7; -m E31 .Extreme 3o' 1re2uency/ <==7<=== >? ;===7;== %m U31 .Ultra 3o' 1re2uency/ <7<= @>? ;==7;= %m ,31 .,ery 3o' 1re2uency/ <=7<== @>? ;=7; %m 31 .3o' 1re2uency/ <==7<=== @>? ;===7;== m -1 .-e$ium 1re2uency/ <7<= ->? ;==7;= m >1 .>igh 1re2uency/ <=7<== ->? ;=7; m ,>1 .,ery >igh 1re2uency/ <==7<=== ->? ;==7;= cm U>1 .Ultra >igh 1re2uency/ <7<= G>? ;=7; cm S>1 .Super >igh 1re2uency/ <=7<== G>? ;=7; mm E>1 .Extreme >igh 1re2uency/  The micro'ave fre2uency range is ( i(e(& micro'ave ra$io signal propagates in U>1 an$ S>1 ra$io +an$( The mostly use$ common fre2uencies for micro'ave propagation are & A& & & & ;;& ;<& ;& ;& <& < G>?( 1riis Transmission formula for micro'ave signal propagation 'here& 5 #eceive po'er 5 Transmit Fo'er 5 Transmitting antenna gain 5 #eceiving antenna gain 5 1ree Space 3oss .path loss/ 5 Transmission line loss +et'een transmitter an$ transmitting antenna 5 Transmission line loss +et'een receiver an$ receiving antenna  The terms 1S3& "t an$ "r are the one 'hich constitutes the attenuation of micro'ave signal( is measure$ in ->? an$ is measure$ in %m

). C#u** o+ Attnu#tion

#$ %ong distance Attenuation  The signal gets attenuate$ as it propagates through the me$ium an$ longer the $istance it travels the more it gets attenuate$ an$ *nally after propagating through a long $istance& the signal get vanishe$ completely( So& as the signal travels& it gets attenuate$ exponentially( )n general& the maximum transmission $istance +et'een t'o stations is = %m +ut 'hen the signal propagates through the reecte$ surfaces such as rivers& oceans& la%es& sea etc(& then the maximum $istance it can propagate is only a+out < %m( Experiment: Transmission +et'een t'o islan$s "n experiment 'as carrie$ out for  months to see the propagation characteristics of the micro'ave signal over the seas( The t'o micro'ave stations 'ere esta+lishe$ on the t'o islan$s locate$ at = %m apart from each other( "fter  months& it is conclu$e$ that it is important to put the antenna of the high station at a place much higher than that of the lo'er station +ecause the signal gets very a4ecte$ +y the incoming 'aves an$ the reecte$ 'aves 'hile propagating over the surface of the sea( So the signal gets signi*cantly attenuate$ if the signal propagates just a+ove the surface of the sea thatHs 'hy itHs +etter to let the signal propagates much a+ove the surface of the sea( So for this 'e have to put the micro'ave antenna at a signi*cant height( "lso the large si?e antennas shoul$ +e chosen for long $istance communication( # Atmosp&eric Attenuation ((; #ain "ttenuation "nother important source of micro'ave signal attenuation is rain( Ihen the rain rate intensity is high& then the micro'ave signal gets signi*cantly attenuate$( 1or example& it is o+serve$ that at high rain intensity .;= mm0hr/& the fa$ing of #1 signal at (A G>? reache$ the value =(= $B0%m( So even if the transmission $istance is near an$ the transmitte$ po'er is large enough& the signal 'ill +e attenuate$ in a very signi*cant amount $ue to heavy rain that the lin% +et'een the t'o stations may +rea% $o'n( The attenuation +ecomes signi*cant at higher f re2uencies an$ more precisely saying at fre2uencies greater than ;= G>?( "t higher fre2uencies& the signal can get attenuate$ up to ; $Bm0%m $ue to heavy rain fall( (( "ttenuation $ue to fog& 'in$& sno'& hurricane etcJ  There are other factors that a4ect the signal $egra$ation such as $og& 'in$& hurricane etc( +ut these e4ects are not that much signi*cant( #' Attenuation due to trees "nother factor that engen$ers the signal attenuation is the tree( The signal often has to propagate via $ense forest( The a+sorption of signal is signi*cant 'hile propagating through the $ense forest( )solate$ trees are not the pro+lem for micro'ave signal as their in$ivi$ual e4ect of attenuation is very small( )n one 



experiment& it is o+serve$ that the trees having 'et leaves can cause huge attenuation as compare$ to the trees +earing the $ry leaves( )t is o+serve$ that the signal can get attenuate$ up to =(A $B0m at < G>?( So there is a huge path loss if the signal passes through several hun$re$s meters through the  jungle( #( Attenuation due to defective parts of microwave communication system "ttenuation can also +e occurre$ $ue to the $efective parts of micro'ave communication system such as micro'ave antenna& 8DU .8ut$oor Unit/& )1 ca+le .the ca+le connecting 8DU an$ the )DU .)n$oor Unit/& connectors etc( )f thereHs something 'rong 'ith the a+ove mentione$ e2uipments then either the signal canHt +e transmitte$ or receive$ or may +e the signal propagating 'ill +e attenuate$ an$ the $egree of attenuation $epen$s upon the $egree of seriousness of the $efects( 1or example& if thereHs a heavy rain an$ $ue to 'hich the 'ater goes insi$e 8DU& then the signal may +e attenuate$ in a signi*cant amount& also if thereHs something pro+lem in connectors& )1 ca+les etc& then the signal goes un$er attenuation( Usually& )1 ca+le use$ to connect 8DU an$ )DU is a coaxial ca+le 'hich has normally an attenuation of = $B at <= ->? 'hile o'ing through =m of  $istance& +ut the signal here is electrical instea$ of ra$io +ecause only the electrical signal can pass through the fee$er ca+le .= ohm coaxial ca+le/(  The part 'here the rain $rop .'ater/ can a4ect 1lange .8ptical me$ium for transmission/

,. I-#ct* o+ Attnu#tion on co--unic#tion *"*t There are several impacts of signal attenuation on communication system( They are $iscusse$ +elo': '#$ )ossi!ility of !reak down of Radio link   The signi*cant amount of signal attenuation can result in +rea% $o'n of the ra$io lin% +et'een the t'o stations( )f there is a signi*cant attenuation an$ the #S3 .#eceive Signal 3evel/ or receive$ po'er excee$s the fa$e margin& then the ra$io lin% 'ill +rea% $o'n an$ hence the communication system is completely interrupte$( '# *ost of use of numerous repeaters used for signal en&ancement  1or very long $istance communication& the signal has to propagate carrying enough po'er level for the receiver to receive the signal( But as alrea$y $iscusse$& the micro'ave signal can propagate only up to = %m( So if one has to esta+lish the micro'ave lin% at a greater $istance than = %m& there comes the nee$ of po'er ampli*er or repeater 'hich regenerates the signal an$ the signal can again propagate = %m further( So if the transmission $istance is so far& a num+er of repeaters 'ill +e nee$e$ 'hich ma%es the communication system costly( 8DU -icro'ave antenna Fart 'here 'ater can a4ect #egenerate$ signal traveling to main $estination Station use$ especially for

transmitting signal targete$ to / station #eceiver station #epeater station

0. So%ution to Attnu#tion (#$ Selection of appropriate radio frequency   The attenuation of ra$io signal is $irectly proportional to the fre2uency( That is 'here " is attenuation an$ f is the fre2uency of micro'ave signal( "lso attenuation is $irectly proportional to the $istance travelle$ +y the signal  This means that if 'e use the higher fre2uency& there 'ill +e more attenuation( So if the transmission $istance is short then the higher fre2uency can +e use$ as there is not much impact of attenuation at short $istance +ut if the transmission $istance is long& then the lo'er fre2uency must +e use$ instea$ of higher fre2uency +ecause there is a signi*cant impact of attenuation $ue to higher fre2uency at longer $istance( 1or example& if the lin% $istance is a less than  %m& then the higher fre2uency antenna such as ; G>?& ; G>? or higher than that can +e use$ for the esta+lishment of the micro'ave lin%( )f the lin% $istance is  %m 7 ; %m& 'e can use only up to ; G>? micro'ave antenna an$ not higher than that +ecause ; %m $istance is 2uite enough for the signal to go un$er signi*cant attenuation at higher fre2uencies than ; G>?( "n$ if the transmission $istance is aroun$ ; %m 7 < %m& then much lo'er fre2uencies  G>? or K G>? micro'ave antenna can +e use$ to counter+alance the e4ect of attenuation travelling through the long $istance( (# +se of Repeaters, " repeater is a net'or% $evice use$ in transmission system to regenerate or replicate the signal $istorte$ +y transmission loss( )t acts as a relay +et'een the t'o stations 'hen it is impossi+le for ra$io signal to reach up to another station 'ith enough po'er level( The analog repeater can amplify the signal 'hereas the $igital repeater can reconstruct the signal to its original 2uality( Iith the use of repeater& 'e can have a longer $istance communication possi+le( "lso 'e can use higher fre2uency antenna for transmission instea$ of using lo'er fre2uency micro'ave antenna( Ie can esta+lish the repeater station in +et'een t'o far stations an$ relay micro'ave ra$io signal +et'een theses t'o stations 'ithout the signi*cant attenuation of signal( No signal +eyon$ this line Co?H not suLcient po'er +eyon$ this line $ue to attenuation(

/   Y  "lso& 'ith the use of the repeater& one can esta+lish the micro'ave lin% +et'een the t'o sites 'hich 'oul$ have not +een possi+le 'ithout the use of the repeater $ue to 38S .3ine 8f Sight/ pro+lem( This is illustrate$ in the *gure +elo':

1rom *gure it is clearly seen that $ue to 38S pro+lem& there is no chance of esta+lishing the micro'ave lin% +et'een the stations M an$ ! +ecause there is a huge o+struction .hill/ in +et'een them 'hich prevents the signal of M to pass through it to reach up to !( So +y esta+lishing a ne' station  at the top of the hill as sho'n& it can set up the lin% to +oth stations M an$  'ith it an$ e2uivalently esta+lishing the lin% in +et'een these t'o sites(  The station  is in 38S of +oth stations M an$ ! an$ hence can easily relay the signal +et'een them( (#' Ma-imi.ing transmitted power  "nother solution to attenuation is +y maximi?ing transmitte$ po'er( Ie %no' that the po'er transmitte$ is $irectly proportional to the $istance it can travel carrying signi*cant amount of po'er level( )t is useful 'hen 'e $onOt 'ant to use the lo'er fre2uency antenna an$ also 'e can not re$uce the transmission $istance( )n this case 'e get the solution only +y maximi?ing the transmitte$ po'er( 1or an example& if 'e have to transmit the signal over ;= %m transmission $istance using ; G>? micro'ave antenna& 'e have to a$just the transmit po'er of micro'ave antenna at a maximum value .;P $Bm/& only then it is possi+le to esta+lish the lin%& other'ise less transmitte$ po'er can not reach up to another station situate$ at ;= %m apart from the transmitting station( 8f course& there is a $ra'+ac% of maximi?ing the transmitte$ po'er& there may +e interference to other stations locate$ near +y( But 'e can transmit the po'er 'ith its maximum value 'hen there is no other stations near +y or 'hen it is more important to esta+lish the lin% an$ 'e can $o so at the cost of the interference to another stations locate$ near +y( (#( Increasing t&e fade margin Generally& in real 'orl$ communication& fa$e margin is one of the important things to +e consi$ere$ 'hile $esigning the ra$io transmission system( 1a$e margin .here/ means the range of receive po'er level up to 'hich the signal can +e caught +y the station an$ hence the lin% $oes not +rea% $o'n( 1or example& 1rom $esign value& if #S3 5 7 A $Bm& fa$e margin 5 = $Bm an$ if $ue to heavy rain or some other factor the signal gets attenuate$ heavily an$ the receive po'er level at receiver is only 7= $Bm& then the lin% 'ill still remain up +ecause of the = $Bm fa$e margin( Due to the fa$e margin of = $Bm& the lin% 'ill remain up even if 'e receive the signal 'ith a po'er of 7 . AQ= 5 / $Bm( So& it is al'ays +etter to have a slightly larger fa$e margin in micro'ave communication +ecause there is a fre2uent uctuation of signal po'er level $ue to various factors(

  Y  / #epeater 1ig( )llustration of the use of #epeater in hilly areas

(#/ +sing perfect and well installed radio equipments

"s alrea$y $iscusse$ a+ove a+out the impact of $efective parts of communication system& one shoul$ ta%e care a+out the proper installation of -I ra$io e2uipments an$ 'ell chec% up of all the net'or% elements +efore putting the stations on air( -ay +e sometimes& the 8DU $uring heavy rain& canOt 'or% properly if it is not properly installe$ an$ the connectors of 8DU are not properly ma$e an$ 'rappe$ 'ith 'eather proof tapes an$ insulation tapes etc( The 'eather proof tapes an$ the insulation tapes prevent 8DU from +eing a4ecte$ +y the 'eather such as moisture& rain& sno' etc& other 'ise 8DU ange is highly prone to +e a4ecte$ +y rain $rop( "s $iscusse$ earlier& the transmission line .fee$er ca+le/ can also +e the portion 'here there is an attenuation of  signal& con*rming 'ell installation of all these ca+les an$ connectors& the attenuation of the ca+le can +e minimi?e$(

2. Conc%u*ion Di4erent types of causes of attenuation of micro'ave signal 'ere un$erstoo$ clearly an$ hence various %in$s of  techni2ues to counter+alance the e4ects of attenuation 'ere propose$ clearly in this paper(