Design a Planar Band-Pass Filter in Hairpin Configuration Mohammad Ismail Hossain May 13, 2012
Design a Planar Band-Pass Filter in Hairpin Configuration
Report Submitted By
Mohammad Ismail Hossain Communicati Communications, ons, Systems and Electronics Electronics School of Engineering and Science Jacobs University Bremen
[email protected] May 13, 2012
Course: RF and Microwave Component and System Design (Lab).
Course Instructor: Prof. Dr. Sören Peik
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Abstract In this report, we address to design a planer band-pass band-pass filter in hairpin configuration. configuration. The scope of this project presented analyze, simulation, fabricate and measurement for microwa microwave ve hairpin hairpin filter design. design. As we know know hairpi hairpin n filter filter is one of the most popular microwave frequency filters because it is compact and does not require groundi grounding. ng. A combin combinati ation on of five five pole hairpin hairpin resonato resonators rs is designed designed to operate operate at center frequency of 2.40 GHz with a bandwidth of 200 MHz and 2.35 – 2.45 GHz frequency frequency band, respectively respectively.. This frequency is presenting for wireless LAN applicaapplication and operates in the ISM band (Industrial, Scientific and Medical) application. In order to design hairpin filter several steps are considered that including by determining filter specification, order of filter, low pass filter prototype elements, low pass to band-pass transformation, physical dimension (width, spacing, length) and wavele wa velength ngth guide. All simulations simulations are performed p erformed by using “Advanced “Advanced design System (ADS)” software. software. The Rogers RO4003 substrate with dielectric constant constant 3.55 and 32 mil of thickness is used to fabricate by using etching process. Improvement technique is introduced to get better response for scattering parameter. Finally, the results from the implemented filter are analysed by using Network Vector Analyzer.
Contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 Intr Introdu oduct ctio ion n 1.1 1.1 Intro Introduc ducti tion on . . . . . . . . . 1.2 1.2 Objec Objectiv tives es . . . . . . . . . . 1.3 1.3 Prio Priorr to work ork . . . . . . . . 1.4 1.4 Projec Projectt Method Methodol ology ogy . . . . 1.4.1 1.4.1 Filter Filter Specificat Specification ionss .
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2 Theore Theoretic tical al Bac Backgr kgroun ound d 2.1 2.1 Back Backgro groun und d Study Study . . . . . . . . . . . . . . . . 2.2 2.2 Filt Filter er . . . . . . . . . . . . . . . . . . . . . . . . 2.2. 2.2.11 Basi Basicc Filt Filter er Types Types . . . . . . . . . . . . 2.2.2 2.2.2 Applic Applicatio ations ns of Filters Filters . . . . . . . . . . 2.2.3 2.2.3 Classi Classificat fication ionss by by Respon Response se Type Type . . . . 2.3 2.3 Micro Microst strip rip Line Line . . . . . . . . . . . . . . . . . . 2.3.1 2.3.1 Coupled Coupled Microstr Microstrip ip Lines Lines . . . . . . . . . 2.4 Filter Filter Protot Prototype ype and Trans Transform formati ations ons . . . . . . 2.4.1 Low-Pass Low-Pass to Band-Pass Band-Pass Transformation ransformation .
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3 Practi Practical cal Procedu Procedures res 3.1 3.1 Scope Scope of the the wor work k. . . . . . . . . . . . . . . . . . . . . . . . . 3.2 3.2 Desi Design gn Proced Procedure uress . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1 3.2.1 Low-p Low-pass ass protot prototype ype design design with with lumped lumped elemen elements ts . . . 3.2.2 Impedance and Frequency Transformations ransformations . . . . . . . 3.2.3 Low-Pass Low-Pass to Band-Pass Band-Pass Transformation ransformation . . . . . . . . . 3.2.4 3.2.4 Lumped Lumped to Coupl Coupleded-Line Line Trans Transform formatio ations ns . . . . . . . 3.2.5 Coupled-Line Coupled-Line to Hairpin Hairpin Configuration/ Configuration/ Planar Circuit Circuit 3.2.6 3.2.6 Design Designed ed Layout Layout . . . . . . . . . . . . . . . . . . . . . 4 Resu Result ltss
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5 Conc Conclu lusio sion n 26 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
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Chapter 1 Introduction 1.1 1.1
Intr In trodu oduct ctio ion n
A band-pass filter is an electronic device that allows signals between two specific frequenc frequencies ies to pass through, through, and discrim discriminat inates es any any unwa unwant nted ed signals signals out of the desired frequencies. frequencies. The Advance Advance of telecommunication telecommunication system has enhanced the need of more sophisticated devices in order to support the variety of the applications. In order to meet the consumers need, a microwave band-pass filter with a compact size, high quality in performance together with a low cost is required. Since filter is the most important device in communication system as well as band-pass filters. Band-pass filters are used as frequency selective devices in many RF and microwa crowave ve applic applicatio ations. ns. Filters Filters are realized realized using lumped lumped or distri distribute buted d circuit circuit elements. ments. However However with the advent advent of advanced advanced materials and new fabrication fabrication techniques, microstrip filters have become very attractive for microwave applications becaus becausee of their their smal smalll size, size, low low cost cost and better better perform performan ance. ce. There There are vario various us topologies to implement microstrip band-pass filters such as end-coupled, parallel coupled, coupled, hairpin, inter-digital inter-digital and combline combline filters. This project represents the design of a hairpin microstrip band-pass filter. The hairpin resonator filter is one of the most popular microstrip filter configurations used in the lower microwave frequencies. It is easy to manufacture because it has open-circ open-circuite uited d ends that require require no groundi grounding. ng. Its form is derive derived d from the edge-coupled resonator filter by folding back the ends of the resonators into a “U” shape. This reduces the length and improves the aspect ratio of the microstrip significan nificantly tly as compare compared d to that of the edge-coupl edge-coupled ed configura configuration tion.. There There are many substrates with various dielectric constants that are used in wireless applications. Those with high dielectric constants are more suitable for lower frequency applications tions in order order to help minimi minimize ze the size size [1]. [1]. In order to increas increasee the band-wid band-width th of end-coupled microstrip band-pass filter parallel coupled microstrip band-pass filter (PCM-BPF) is considered and resonators are positioned so that adjacent resonators are parallel to each other along half of their length. This parallel arrangement gives relativ relatively ely large couplin couplingg for a given given spacing spacing bet b etwe ween en resonato resonators rs [2]. [2]. But this new configuration was too long considering the frequency and the order of the filter. To solve this problem hairpin-line filter is developed. Digital broadcasting is a set of transmission standards that aim to broadcast
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signals signals in digital form with a specific slant. slant. The mode of distributions distributions can be through a medium of satellite, terrestrial or cables. Recently, many countries worldwide are moving moving towards towards a revolutionar revolutionary y change to digital broadcasting. broadcasting. The digital signal broadcasting begins from a transmitter located at Simple Hairpin Band-pass Filter. In our case, we need to design, built and measure a typical microwave circuit and all components will be connected together to accomplish our job, we can find below the block diagram of RF communication system.
Figure- 01: Block diagram of RF communication system. Hence, microwave band-pass filter used in many RF/microwave applications is the fundamental component that contributes the overall performance of a communication nication system. system.
1.2
Objec bjecti tiv ves
The objectives of this project are:1. To desig design n and sim simulati ulation on hairpi hairpin n bandband-pa pass ss filter filter at 2.40 2.40 GHz GHz operati operating ng frequency, 5th order Chebychev 0.5 dB ripple and 200 MHz of bandwidth using ADS simulation software. 2. To fabricate and measurement measurement the microstrip microstrip filter fabricated on the Rogers RO4003c with thickness of 32 mil by using etching technique. 3. To compare between simulation and measurement result.
1.3
Prior to work
Nowadays filters in the market are more complex. The hairpin filter is better than other other filters filters because it is compact compact and does not require require grounding. grounding. This This filter filter also also produces high frequency a wide band filter and comparatively low cost.
1.4 1.4
Proje Project ct Meth Methodo odolo logy gy
In order to design, built and measure the 5th order chebychev band-pass filter in hairpin configuration following steps are considered.
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Figure-02: Design flowchart of hairpin band-pass filter. In this project mainly number of four major steps are required:1 Literature Review Gather the information about the project via Internet, journals, magazines, published work and reference books. Study of the software implementation (ADS). Make research to know more detail about designing hairpin filter according all parameters. parameters. •
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2. Calculation, Analysis and Simulation Analyzed and calculated all parameters that related to design the step impedance hairpin resonance. Using ADS software to observe the frequency and scattering response for hairpin filter. •
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3. Hardware Development and Implementation Then proceed to designing microstrip filter using etching technique and measure using spectrum analyzed. Lastly, compare between simulation and measurement results. •
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1.4. 1.4.1 1
Filt Filter er Speci Specific ficat atio ions ns
The filter is specified as follows: Parameter Frequency Band Bandwidth Type Insertion Loss Return Loss
Symb ol Value f 2.35-2.45 BW 20 0 5 order Chebychev IL 3 RL 12
Unit Tolerance Remarks GHz MHz 0.5dB Bandwidth 0.5dB Ripple dB max in Pass Band dB min in Pass Band
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Chapter 2 Theoretical Background 2.1 2.1
Bacckgro Ba kgroun und d Stud Study y
The use of microstrip in the design of microwave microwave components and integrated integrated circuits has gained tremendous popularity since the last decades because microstrips can operate in a wide range of frequencies. frequencies. Furthermore, urthermore, microstrip is lightweigh lightweight, t, easier fabrication fabrication and integration, integration, and cost effective. Many researchers researchers have presented numerous equations for the analysis and synthesis of microstrip. However, along with the sophistication sophistication comes with a high price tag, copy protection protection schemes and training training requirements that create difficulties for exploratory usage in an academic environment. ment. Therefore, Therefore, a low cost, user-friendly user-friendly,, open op en source system software software package is needed that can be used as an effective training aid on microstrip filters design.
2.2
Filter
A microwave filter is a two-port network used to control the frequency response at a certain point in a microwa microwave ve system by providing providing transmission transmission at frequencies frequencies within the pass-band of the filter and attenuation in the stop-band of the filter [6]. Filt Filters ers may be clas classi sified fied in a numb number er of wa ways ys.. An exampl examplee of one such such clasclassificati sification on is reflectiv reflectivee versus versus dissipati dissipative ve.. In a reflectiv reflectivee filter, filter, signal signal rejection rejection is achieved by reflection the incident power, while in a dissipative filters are used in most applications. The most conventional description of a filter is by its frequency characteristic such as low-pass, high-pass, band-pass or band-reject (notch).
2.2. 2.2.1 1
Basi Ba sicc Filt Filter er Types ypes
In microwave communications, there are mainly five types of filter are used which are briefly described in the following [4]:
2.2.1.1 2.2.1.1
Low-P Low-Pass ass Filter Filter
Low-pass filter networks transmit all signals between DC and some upper limit wc , and attenuate all signals with frequencies above wc . They They are realized realized by using using a cascade cascade of series series inducto inductors rs and shunt shunt capacito capacitors. rs. The frequency frequency range of the filter
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specificat specification ion has been b een divided divided into three areas. areas. The passband passband extends extends from zero frequency (dc) to the passband edge frequency f pass, and the stop-band extends from the stop-band edge frequency f stop stop to infinity. These two bands are separated by the transition band that extends from f pass to f stop stop .
2.2.1.2 2.2.1.2
High-P High-Pass ass Filter Filter
High-pass filter pass all signals with frequencies above the cut-off value wc to the load with minimum loss and reject signal with frequencies frequencies below wc . High-pass filter networks are realized by using a cascade of series capacitors and shunt inductors. In this case the passband extends from f pass to infinity and is located at a higher frequency than the stop-band which extends from zero to f stop stop. High-pass filters are used when it is important to eliminate low frequencies from a signal.
2.2.1.3 2.2.1.3
Band-P Ban d-Pass ass Filter Filter
The band-pass filter shows the signal is transferred to the load in a band of frequencies between the lower cut-off frequency, wc1 , and the upper cut-off frequency, wc2 . Between the lower and upper cut-off frequency is the centre frequency, w0 , defined by the geometric mean of wc1 and wc2 [3]. [3]. A band-pas band-passs filter filter will will pass pass a band band of frequencies while attenuating frequencies above or below that band. In this case the passband exists between the lower passband edge frequency f pass1 and the upper passband edge frequency f pass2 . A band-pass band-pass filter filter has two two stop-band stop-bands. s. The lower lower stop-band extends from zero to f stop stop1 , while the upper stop-band extends from f stop stop2 to infinity .
2.2.1.4 2.2.1.4
Band-R Ban d-Rejec ejectt (Sto (Stop) p) Filter Filter
The band-reject band-reject filter is a complement complement of the band-pass filter. The signal experiences high loss between wc1 to wc2 , hence the name band-stop or band-reject. In this case the band of frequencies frequencies being rejected is located between the two two pass-bands. The stop-band exists between the lower stop-band edge frequency f stop stop1 and the upper stop-band stop-band edge frequency frequency f stop stop2 . The band-stop filter has two pass-bands, the lower passband extends from zero to f pass1 , while the upper passband extends from f pass2 to infinity .
2.2.1.5 2.2.1.5
All-Pa All-Pass ss Filter Filter
The all-pass filter allows the signal amplitude for all frequencies to pass through the network network without any significant significant loss. This network network has no frequency selective pass band or stop band. Typically Typically frequency and amplitude responses for these difference difference types are shown in figure-3. In additional, an ideal filter displays zero insertion loss, constant group delay over the desire pass-band and infinite rejection elsewhere. However, in practical filters deviate from these characteristics and the parameters in the introduction above are a good measured of performance.
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Figure-3: Amplitude response of different filter types. (http://www.cs.sfu.ca/~tamaras/filters/Ma (http://www.cs.sfu.ca/~tamaras/filters/Magnitude_Response_Basic.html) gnitude_Response_Basic.html)
The cut-off frequency is typically defined as the frequency at which the power transmitted by the filter drops to one-half (by -3 dB) of the maximum power transmitted in the passband.
2.2. 2.2.2 2
Appl Applic icat atio ions ns of Filt Filter erss
As mentioned above, virtually all microwave receivers, transmitters and so fifth required filters. Typically commonly used circuits that require filters include mixers, transmitters, transmitters, multiplexers multiplexers and the like. Multiplexers Multiplexers are essential essential for channelized channelized receivers. receivers. Therefore, Therefore, system application of filters include radar, communications, communications, surveillance, EMS receiver, Satellite Communication (SATCOM), mobile communications, direct broadcast, satellite systems, personal communication system (PCS) and microwave FM multiplexer. In many instances, such as PCS, miniature filter are a key to realizing realizing require reduction in size. There is, however, however, a significant significant reduction reduction in power handling capacity and an increase in the insertion loss. The former is not a severe limitation in such system, however, and the latter can be compensated for by subsequent subsequent power application.
2.2.3 2.2.3
Classifi Classificat cation ionss by by Respon Response se Type
Based on designing signal processing filters, there are several important classes of filter filter such such as Butterw Butterworth orth filter, filter, Chebysh Chebyshev ev filter, filter, Ellipt Elliptic ic (Cauer) (Cauer) filter, filter, Bessel Bessel filter, Gaussian Gaussian filter, Optimum Optimum "L" (Legendre) filter, Linkwitz-Riley Linkwitz-Riley filter. It was originally intended to be applied to the design of passive linear analogue filters but its results can also be applied to implementations in active filters and digital filters. filters. The class class of a filter filter refers to the class class of polynomi polynomials als from which which the filter is mathemati mathematicall cally y derive derived. d. The order of the filter is the number number of filter filter elemen elements ts
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presen presentt in the filter’s filter’s ladder ladder implem implemen entati tation. on. General Generally ly speaking speaking,, the higher the order of the filter, the steeper the cut-off transition between passband and stopband. In the following some of filters are described shortly.In the following some of filters are described shortly.
2.2.3.1 2.2.3.1
Butter Butterwo worth rth Filter Filter
The Butterworth filter has essentially flat amplitude versus frequency response up to the cut-off frequency frequency. Butterworth Butterworth filters are also known as maximally maximally flat type filters filters and have have the flattest flattest poss p ossibl iblee pass-b pass-band and magnitude magnitude response. response. This This class class of filters approximates the ideal filter well in the pass band. It has a monotonic decrease in gain with frequency in the cut-off region and a maximally flat response below cutoff. Atten Attenuati uation on is -3 dB at the design design cut-off cut-off frequency frequency.. Atten Attenuati uation on bey b eyond ond the cut-off frequency is a moderately steep -20 dB/decade/pole. The pulse response of the Butterworth Butterworth filter has moderate overshoot and ringing. The Butterworth Butterworth filter has characteristic somewhere between Chebychev and Bessel filter. Advantages: Maximally flat magnitude response in the pass-band. Good all-around performance. Pulse response better than Chebyhev. Rate of attenuation better than Bessel. Disadvantages: Some overshoot and ringing in step response.
2.2.3.2 2.2.3.2
Cheby Chebych chev ev Filter Filter
The Chebychev filter, also called the equal ripple filter, gives a shaper cut-off than the Butterw Butterworth orth filter in the pass-b pass-band. and. Both Both Butterw Butterworth orth and Chebyc Chebychev hev filters exhi exhibi bitt larg largee phase phase shif shiftt near near the cutoff cutoff freque frequency ncy.. This This filte filterr respon response se has the steeper initial rate of attenuation beyond the cut-off frequency than Butterworth. This advantage comes at the penalty of amplitude variation (ripple) in the passband. Unlike Butterworth and Bessel response, which have 3 dB attenuation at the cut-off frequency, Chebychev cut-off frequency is defined as the frequency at which the response falls below the ripple band. For even-order filters, all ripples are above the dc-normalized pass-band gain response, so cut-off is at 0 dB. For odd-order filters, all ripple is below the dc-normalized pass-band gain response, so cut-off is at - (ripple) dB. The Chebychev has more ringing in its pulse response than the Butterworth - especially for high-ripple designs. Advantage: Better rate of attenuation beyond the pass-band than Butterworth. Disadvantage: Ripple in pass-band. Considerably more ringing in step response than Butterworth.
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2.2. 2.2.3.3 3.3
Besse Bessell Filte Filterr
For application where the phase is important, the Bessel filter, which is minimal phase shift filter, is used even though its cut off characteristic is not very sharp. The Bessel filter provides ideals phase characteristic with an approximately linear phase phase response response up to nearly cut-off cut-off frequenc frequency y. The Bessel Bessel filter filter has a very very liner phase response but a fairly gentle skirt slope. Due to its linear phase response, this filter has excellent pulse response (minimal overshoot and ringing). Advantage: Best step response-very little overshoot or ringing. Disadvantage: Slower initial rate of attenuation beyond the pass-band than Butterworth. Comparison between Buttherworth, Chebyshev and Bessel filters can be seen in the below figure.
Magnitude and Phase comparison for diffrent types of filter 0 Butterworth Chebyshev Bessel
−1 ) B −2 d ( e d u −3 t i n g a M−4
−5 −6 0 Butterworth Chebyshev Bessel
) g −180 e d ( e s a h P −360
−540 −1
10
0
10
1
10 Frequency (rad/sec)
2
10
3
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Figure-4: Comparison of amplitude response of Butterworth, Chebyshev and Bessel filters. In order to see the difference between different types of filter a matlab code is implemented where center frequency is 2.4 GHz and for Chebyshev 0.5 dB ripple is considered. From the figure-4 we see that ripple for chebyshev filter.
2.3 2.3
Micr Micros ostr trip ip Line Line
As circuits have been reduced in size with integrated semiconductor electron devices, a transmission transmission structure was required that was compatible compatible with circuit circuit construction construction
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techniques to provide guided waves over limited distances. This was realized with a planar form of single wire transmission line over a ground plane, called microstrip1. Microstrip employs a flat strip conductor suspended above a ground plane by a lowloss loss dielec dielectric tric material material.. The size of the circuit circuit can be reduced reduced through through judicio judicious us use of a dielectric constant some 2-10 times that of free space (or air), with a penalty that the existence of two different dielectric constants (below and above the strip) makes the circuit difficult to analyze in closed form (and also introduces a variability of propagation velocity with frequency that can be a limitation on some applications). applications). The advantages advantages of microstrip have have been b een well established, established, and it is a convenient form of transmission line structure for probe measurements of voltage, current and waves. Microstrip structures are also used in integrated semiconductor form, directly interconnected in microwave integrated circuits. Microstrip has a very simple geometric structure the electromagnetic field involved are actually complex.
Figure-5: Figure-5: Single microstrip transmission transmission line (http://qucs (http://qucs.sourcef .sourceforge.net orge.net). ). where l = Length of the element. w =Width of the element. h = Height of the dielectric element. t = Thickness of the element. The microstrip has their own advantages compare to other microwave transmission like waveguide, coaxial cable, strip line etc. and it has also some disadvantages as well. Its advantages and disadvantages as mention as below:Advantages a) To make easier fabricate of circuit complex. b) Smaller size and light. c) Wide bandwidth. d) Good reliability. e) Good reproducibility reproducibility.. Disadvantages a) High attenuation. b) Low power.
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2.3. 2.3.1 1
Coup Couple led d Mic Micros rostr trip ip Lin Lines es
When two transmission lines are close together, because of the interaction of the electro electromagn magneti eticc fields fields of each each line, line, power power can be b e coupled coupled between between the lines. Those Those coupled coupled lines are used used to construc constructt directi directional onal couplers. couplers. General Generally ly,, in design of directi directional onal couplers couplers microst microstrip rip and stripli stripline ne forms forms are used. used. Althoug Although h micros microstrip trip transmission lines do not support TEM and named as quasi-TEM, usually they are assumed to operate in TEM mode. It is important that whether true TEM or not, all parallel line couplers have odd and even mode, and resulting Z 0e and Z 0o (even and odd mode impedances respectively). In the analysis of the directional couplers we will use also eveneven-odd odd mode analysis. analysis. Coupled Coupled microstr microstrip ip lines are shown shown in figure-6.
Figure-6: Figure-6: Coupled microstrip line (http://qucs. (http://qucs.sourcefo sourceforge.net). rge.net). The equations for the coupled microstrip lines are shown in the below which are used in our project as well. Z 0 J 1 =
Z 0 J n =
Z 0 J N N +1 +1 =
∆
π , 2g1
π∆
√ 2 g
n−1 gn
(2.1)
,
π∆ , 2gN gN +1 +1
(2.2)
(2.3)
From above equations we can obtaineven and odd mode characteristic impedances. Z 0e = Z 0 [1 + J Z 0 + (J Z 0)2 ],
(2.4)
Z 0o = Z 0[1 − J Z 0 + (J Z 0 )2 ].
(2.5)
where, Z 0 = characteristic Impedance of the line, J = admittance inverter, ∆= relative bandwidth, g = filter prototype and n = 2,3,4.....N.
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2.4
Filter Filter Protot Prototype ype and and Tran Transfo sforma rmatio tions ns
Prototype filters are electronic filter designs that are used as a template to produce a modified modified filter design for a particu particular lar applicati application. on. They are an example example of a non dimensionality design from which the desired filter can be scaled or transformed. They are most often seen in regards to electronic filters and especially linear analogue passive filters. However, in principle, the method can be applied to any kind of linear filter or signal processing, including mechanical, acoustic and optical filters. Filters are required to operate at many different frequencies, impedances and bandwidths. The utility of a prototype filter comes from the property that all these other filters can be derived from it by applying a scaling factor to the components of the protot prototype. ype. The filter design design need thus only be carried carried out once in full, full, with other filters being obtained by simply applying a scaling factor. Especially useful is the ability to transform from one band form to another. In this case, the transform is more than a simple scale factor. Band form here is meant to indicate the category of passband that the filter possesses. The usual band forms are low-pass, high-pass, bandpass bandpass and bandstop, bandstop, but others others are possible. possible. In particula particular, r, it is possible possible for a filter filter to have have multipl multiplee pass pass bands. bands. In fact, in some treatmen treatments, ts, the bandstop bandstop filter is considered to be a type of multiple passband filter having two pass bands. Most commonly, the prototype filter is expressed as a low-pass filter, but other techniques are possible. For the specific purpose of this project 0.5 dB Chebyshev filter, filter prototypes are considered from the following table: Table-1: 0.5-dB Chebyshev LC Element Values. Order Rs 5 1.0
g1 1.8068
g2 1.3025
g3 2.6914
g4 1. 3 0 2 5
g5 1. 8 0 6 8
These prototype values are applicable for 1 rad/sec cut-off frequency and when source and load impedance are 1 ohms. From these prototypes prototypes LC value it is possible to switch other filters like high-pass, band-pass, band-stop etc.. In order to achieve low-pass filter scaled to 50 ohms and specific cut-off frequency then below these equations are necessary.
L =
C =
2.4.1
R0 L , ωc
(2.6)
C . R0 ωc
(2.7)
Low-P Low-Pass ass to Band-Pa Band-Pass ss Transf Transformat ormation ion
In order to convert low-pass filter to band-pass filter numbers of two conditions are maintained. •
All capacitors become parallel resonators and
•
All inductors become series resonators.
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Figure-6: Low-pass to band-pass conversion. For this conversion two equations are considered in the below. For L, R0 L , ωc BW
(2.8)
BW . R0 Lωc
(2.9)
R0 BW , ωc C
(2.10)
C . R0 BW ωc
(2.11)
L =
C =
And for C,
L =
C =
where, BW is the relative bandwidth.
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Chapter 3 Practical Procedures 3.1
Sco Sc ope of the the work
Our main goal is to design a 5th order Chebyshev band-pass filter in hairpin configuration with a cut-off frequency of 2.4 GHz, 0.5dB ripple and an impedance of 50 for both source and load.
3.2 3.2
Desi Design gn Proce Procedu dure ress
In order to design the filter with the specifications mentioned above, the following procedures are followed: 1. Low-pass prototype design with lumped elements. 2. Impedance and frequency transformations. 3. Low-pass to band-pass transformations. 4. Lumped elements to coupled-line transformations. 5. Coupled-line to hairpin configuration/ planar circuit design. 6. Layout, etching, and testing. In the following, each of these steps are discussed with some details and difficulties while the implementat implementation. ion.
3.2.1 3.2.1
Low-p Low-pass ass proto protottype design design with with lumped elem elemen ents ts
Using table-1, low-pass prototype filter is designed where the cut-off frequency is 1 rad/sec. rad/sec. For this this design design source and load impedances impedances are 1 ohm. This This is applicabl applicablee for the 5th order low-pass Chebyshev filter with 0.5 dB ripple. Designed circuit can be seen as following figure-7:
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Figure-7: Low-pass prototype filter with lumped elements. Note that number of L-C components equals the order of the filter (in our case, we have 5 L-C elements for the 5th order filter) and g1=g5 and g2=g4. From here we are intere intereste sted d to perform perform simula simulatio tion n for scattering scattering parameters parameters.. After After running running the simulation, we get the following response in the figure below.
Figure-8: Frequency response for low-pass prototype filter. Simulations are performed for frequency range 0 Hz to 2 Hz and here value of ωc is 1 rad/sec. So, from here we get the cut-off frequency 160 mHz and we are getting same same response response in the figure-8. figure-8. For 160 mHz cut-off cut-off frequenc frequency y we obtain obtain value alue of S(1,1) is -2.701 dB. we can also see the equal ripple in the beginning for S(1,1).
3.2.2
Impedance Impedance and and Frequency requency Transformat ransformations ions
By using the impedanc impedancee and frequency frequency transforma transformation tion equations equations no. 2.6 and 2.7 ment mentio ioned ned in chapt chapter er 2. There Therefo fore, re, new valu values es of the the L-C L-C eleme element ntss of the the lowlowpass prototype can be calculated such that the low pass filter matches the required
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specifications of the cut-off frequency of 2.4 GHz and RL = RS = 50Ω with the same design structure of the low-pass low-pass prototype. prototype. Table with the new parameters values values are shown below. Table-2: New values after impedance and frequency transformation. Order 5 C 1 2.398 pF
C1 L1 1.8068 1.3025 L1 C 2 4.322 nH 3.57 pF
C2 L2 C3 2.6914 1.3025 1. 8 0 6 8 L2 C 3 R0 4.322 nH 2.398 pF 50 Ω
After assigned new parameters value our low-pass filter look like in the below circuit.
Figure-9: Lumped low-pass 5th order Chebyshev filter. After performing simulation we see the same response like before and for cut-off frequency frequency 2.4 GHz we obtain value value of S(1,1) is -2.99 dB. We We see the effect of response in the figure below.
Figure-10: Lumped low-pass frequency response. Simulation Simulationss are performed for frequency range 0 to 10 GHz. We observe that the marker on the graph indicates the intersection of the S11 and S12 which represents the value value of the cut-off cut-off frequency frequency.. It can be seen that the cut-off frequenc frequency y is 2.4 GHz as required.
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3.2.3
Low-P Low-Pass ass to Band-Pa Band-Pass ss Transf Transformat ormation ion
The low-pass to band-pass transformation illustrated in figure-6 and we can see that C elements become parallel resonators and L elements become series resonators. By using using equations equations no. 2.8, 2.8, 2.9, 2.9, 2.10 and 2.11 we achie achieve ved d lumped lumped elements elements for 5th order Chebyschev Chebyschev band-pass band-pass filter. Values of lumped elements can be found in the below table as well as circuit diagram. Table-3: Elements value of 5th order band-pass filter. C1(pF) C1(p F) L1(n L1(nH H) C2(p C2(pF) F) L2(n L2(nH H) 28.7894 0.153 0.0849 51.885 L3(n L3(nH) H) C4 C4(p (pF) F) L4(n L4(nH H) C5 C5(p (pF F) 0.1027 0.0849 51.885 28.7894
C3(pF) C3(p F) 4 2. 8 8 5 L5(n L5(nH) H) 0. 1 5 3
From the above above table table we see value alue C1=C5, C1=C5, L1=L5, L1=L5, C2=C4 C2=C4 and L2=L5. Here we use 50 ohms for both load and source impedance.
Figure-11: 5th order Chebyshev band-pass filter. Simulations are performed from 2 GHz to 2.9 GHz and after performing simulations lations we see the nice response response for designed designed band-pass band-pass filter. filter. In order to see the bandwidth we marked the position with different marker where S(1,1) and S(1,2) are intercept and we see for marker one 2.301 GHz and for marker 2 it’s 2.501 GHz. For 2.3 GHz frequency we have value of S(1,1) is -3.787 dB and for 2.5 GHz it is -2.696 dB, and we are getting 0.5 dB ripple as well.
Figure-12: Filter response for 5th order band-pass with lumped elements.
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3.2.4 3.2.4
Lumped Lumped to Coupl Coupleded-Lin Line e Tran Transfo sforma rmatio tions ns
We know for microwave circuits, lumped elements do not work properly. Therefore, instead of using lumped element it is replaced by coupled or parallel transmission line line for parallel parallel resonators resonators.. For the first step we conside considerr ideal ideal transmi transmissi ssion on line line then we shifted to misrostrip line where we use /4 transmission lines. So, by using equatio equations ns no. 2.1 to 2.5 we obtain obtain the values alues of coupled coupled transmiss transmission ion lines which which can be found from the table below. Table-4: Elements Value of coupled-transmission lines. n 1 2 3 4 5 6
gn
Z 0 J n
Z 0e (ohms)
Z 0o (ohms)
1. 1.8068 1. 1.3025 2. 2.6914 1. 1.3025 1. 1.8068 1. 1.8068
0.2690 0. 0.08525 0.0699 0. 0.06985 0. 0.08525 0. 0.08525
67.0681 54.6259 53.7393 53.7393 54.6259 67.0681
40.1681 46.1009 46.7493 46.7493 46.1009 40.1681
After getting required values of even and odd impedance for coupled transmission line we designed our circuit which is in the following.
Figure-13: Band-pass filter with ideal transmission line. After performing simulations we still get the nice response using ideal transmission line. We marked the positions too see the values of scattering responses and for 2.3 GHz we get -2.921 dB and for 2.5 GHz it is -2.428 dB of S(1,1) which is quite reasonab reasonable. le. These These responses responses can be b e seen seen in the below below figure. figure.
Figure-14: Filter response for band-pass filter with using ideal transmission lines.
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3.2.4.1 3.2.4.1
Ideal Ideal line to Micros Microstri trip p line transf transform ormati ations ons
In order to implement filter we know in reality ideal filters doesn’t exist so, we need to convert convert ideal line to microstrip microstrip line. Therefore, Therefore, to achieve achieve required required parameters which are applicable for microstrip line we use line calculator tool from ADS software which is shown in the table below. Table-5: Required parameters value of microstrip line. Z 0e (ohms)
Z 0o (ohms)
6 7. 0 6 8 1 5 4. 6 2 5 9 5 3. 7 3 9 3 5 3. 7 3 9 3 5 4. 6 2 5 9 6 7. 0 6 8 1
40.1681 46.1009 46.7493 46.7493 46.1009 40.1681
W (mm) 1.53 1.7 1.8 1.8 1.7 1.53
S (mm) L (mm) 0.35 1 8. 3 1.3 1 8. 6 1.4 1 8. 3 2 1.4 1 8. 3 2 1.3 1 8. 6 0.35 1 8. 3
At first we used MCLIN and we seen that our required bandwidth was reduced after that we use MCFIL and we still get nice response with this configuration. Circuit is illustrated in the following.
Figure-15: Band-pass filter using microstrip line. After doing simulations we see the quite nice response as before and our case it’s reasonable. reasonable. For this case we marked marked the positions and also performed momentum to see the magnitudes and phases for every scattering parameters, these responses are shown shown in the below. below. In the below below figurefigure-16 16 we see see band band width width still still 200 MHz MHz which is from 2.3 GHz to 2.5 GHz, ~0.5 dB ripple.
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Figure-16: Filter response using microstrip line. After generating layout we tried to perform the momentum simulation and we observ observee the scatteri scattering ng paramet parameters ers and losses losses.. Simula Simulation tion result for moment momentum um is performed and we can find the result in the below.
Figure-17: Momentum response for different scattering parameters. If we see the momentum figure, we see the nice required responses for all of scattering scattering parameters for both magnitudes and phases. As shown clearly clearly from the responses, we still have the required filter response.
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3.2.5 3.2.5
Couple Coupled-L d-Line ine to Hairpi Hairpin n Configura Configuratio tion/ n/ Planar Planar CirCircuit Design
Our ultimate goal to design 5th order band-pass filter in hairpin configuration so, we need to convert convert coupled-line coupled-line configuration configuration to hairpin hairpin configuration. configuration. The advantages advantages of hairpin filter are discussed discussed earlier. For manufacturing manufacturing and fabrication fabrication purposes together together with technic technical al advan advantage tages, s, the planar circuit circuit design design is used. In his step, we will design the planar circuit by transforming into planar microstrip lines with ports are connected at the end. Using transmission line tool, the parameters of the microstrip line (width and length) are calculated given the characteristic impedance and the dielectric constant ( εr = 3.55 ) for our material. The T-junction is used for fabrication purpose and design as follows.
Figure-18: Planar design circuit in hairpin configuration. After performing simulation for the first time we observed that our frequency response unlikely unlikely shifted. So, we varied varied the lengths in the schematic hairpin hairpin filter design design until until we get our desired desired filter response using using tuning tuning option. option. After After that we have the quite nice response for our band-pass filter and we marked the positions for 2.3 GHz and 2.5 GHZ. For these frequency points we get values of S(1,1) -2.167 dB and -3.1 -3.193 93 dB respec respecti tive vely ly.. It can can be seen seen that that some some of the the micro microstr strip ip lines lines have widths less than 0.05 mm which is not accepted in our design since the etching machine will be used for manufacturing the circuit can deal with lines with widths not less than 0.05 mm. So, the widths of these lines should be increased, no specific methods methods will be used for this, just “try and error”! error”! such such that we should still still have the “same” performance. After observing observing the circuit simulation simulation we get still 0.5 dB ripple which is marked by m1.
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Figure-19: Filter response in hairpin configuration.
3.2. 3.2.6 6
Desi Design gned ed La Lay yout out
In order to manufac manufacture ture our designe designed d filter filter we have have generate generated d filter filter layo layout. ut. We have generated layout for coupled-line configuration and hairpin configuration. We observe that our designed layout is most likely similar what we expected which as follows.
Figure-20: Generated layout for coupled-line filter.
Figure-21: Generated layout for filter in hairpin configuration. Finally, our desired layout is created for preparing the circuit for etching and manu manufac factur turin ing, g, in the abov above layo layout ut is created created.. We also also see the the 3D view view of our designed filter and it is quite good what we expected.
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Chapter 4 Results After implementing and manufacturing our designed 5th order Chebyshev band-pass filter now we have the hardware view which as follows. We measured our filter with Vector Network Analyzer and we see quite nice frequency response like before.
Figure-22: (a) Implemented real view of BPF, and (b) simulation result from VNA. From the above figure we can see our implemented device that means real manufactured view of our designed microstrip band pass filter in hair configuration and simulation result which is taken from Vector Network Analyzer (VNA). In order to have test and result we see from VNA our resonant frequency is shifted but we are satisfied because we get nice response for chebychev band pass filter and we are getting getting some kind kind of loss loss for measuri measuring ng S12 and S21 due to lossy lossy device. device. In order to manufacture this device we see our manufactured device is connected with two coupled microstrip line which was unexpected, for this reason we disconnected to each each other other to have have better performanc performance. e. After After the board was milled milled to the desired desired pattern, connectors were attached and the filter was measured using Rohde and Schwarz network analyzer. Figure-22 (b) is the through performance (S21) and return loss (S11) of the prototype prototype filter. The measurements measurements show very good agreement agreement with the models. The passband is slightly shifted than predicted by ADS.
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Chapter 5 Conclusion In this project, a band-pass 5th order Chebyshev microwave filter with a cut-off frequenc frequency y of 2.4 GHz is design designed, ed, fabricated fabricated and tested. The circuit circuit is designe designed d using distributed elements and then planar microstrip lines are used.We have seen the coupled-line coupled-line band-pass filter and hairpin band-pass band-pass filter respectively. respectively. The detailed tailed steps are shown, shown, discussed discussed and analyzed. analyzed. The performance performance of the circuit circuit is discus discussed sed basing on the simulati simulations ons performed performed for the response response of the design. design. We get nice results after that if we give more time on this circuit output would more better better than before. before. The filter was designed designed using ADS softwa software re with a resulti resulting ng layo layout ut shown shown in above above figures. This This is the famili familiar ar hairpi hairpin n configura configuratio tion n consist consist-ing of microstrip circuit RF components such as microstrip lines, TEE- sections and coupled lines. To perform optimization optimization runs geometrical parameters parameters were assigned signed to the individua individuall RF-compo RF-componen nents. ts. This This project project reports reports hairpin hairpin filters with improved characteristics over conventional structures using standard design equations. The line widths and spacing can be easily etched using standard fabrication techniques. techniques. Narrower Narrower bandwidths bandwidths have been achieved without without additional components. The structures are validated having close match between the simulated and practica practicall results results.. This This approac approach h can be extende extended d to much much higher higher frequenc frequency y range range without without compromis compromising ing the filter filter performan performance. ce. Althoug Although h we don’t get appropri appropriate ate output due to etch and common problems happened by us during simulation layout. Finally, we can say that we have the total idea to implement RF filter using ADS simulation software and fabrication technique. In our case we used Rogers RO4003 substrate with dielectric constant 3.55 and 32 mil of thickness to fabricate our filter by using etching process.
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Bibliography [1] S. Peik, Lecture Notes “Microwav “Microwavee Filter Design”, 2009. [2] D. Pozar, “Microwav “Microwavee Engineering”, Engineering”, second edition. [3] “Electronic “Electronic Filter Design Design Handbook” [4] Noyan Noyan Kinayman, Kinayman, M. I. Aksun,“Modern Aksun,“Modern Microwav Microwavee Circuits” Circuits” [5] Ian Hunter,”Theory Hunter,”Theory and Design of Microwa Microwave ve Filters” [6] Les Thede,”Practical Thede,”Practical Analog and Digital Filter Design”,Arte Design”,Artech ch House, Inc. 2004
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