Design a Planar Band-Pass Filter in HairpinConfiguration

Mohammad Ismail Hossain

May 13, 2012

Design a Planar Band-Pass Filter in Hairpin Configuration

Report Submitted By

Mohammad Ismail Hossain

Communications, Systems and Electronics

School of Engineering and Science

Jacobs University Bremen

m.hossain@jacobs-university.de

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 filter in hairpin configuration.The scope of this project presented analyze, simulation, fabricate and measurementfor microwave hairpin filter design. As we know hairpin filter is one of the mostpopular microwave frequency filters because it is compact and does not requiregrounding. A combination of five pole hairpin resonators is designed to operate atcenter frequency of 2.40 GHz with a bandwidth of 200 MHz and 2.35 – 2.45 GHzfrequency band, respectively. This frequency is presenting for wireless LAN applica-tion and operates in the ISM band (Industrial, Scientific and Medical) application.In order to design hairpin filter several steps are considered that including by de-termining filter specification, order of filter, low pass filter prototype elements, lowpass to band-pass transformation, physical dimension (width, spacing, length) andwavelength guide. All simulations are performed by using “Advanced design Sys-tem (ADS)” software. The Rogers RO4003 substrate with dielectric constant 3.55and 32 mil of thickness is used to fabricate by using etching process. Improvementtechnique is introduced to get better response for scattering parameter. Finally, theresults from the implemented filter are analysed by using Network Vector Analyzer.

Contents

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1 Introduction 31.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.3 Prior to work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.4 Project Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.4.1 Filter Specifications . . . . . . . . . . . . . . . . . . . . . . . . 6

2 Theoretical Background 72.1 Background Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.2 Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2.1 Basic Filter Types . . . . . . . . . . . . . . . . . . . . . . . . 72.2.2 Applications of Filters . . . . . . . . . . . . . . . . . . . . . . 92.2.3 Classifications by Response Type . . . . . . . . . . . . . . . . 9

2.3 Microstrip Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112.3.1 Coupled Microstrip Lines . . . . . . . . . . . . . . . . . . . . . 13

2.4 Filter Prototype and Transformations . . . . . . . . . . . . . . . . . . 142.4.1 Low-Pass to Band-Pass Transformation . . . . . . . . . . . . . 14

3 Practical Procedures 163.1 Scope of the work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163.2 Design Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.2.1 Low-pass prototype design with lumped elements . . . . . . . 163.2.2 Impedance and Frequency Transformations . . . . . . . . . . . 173.2.3 Low-Pass to Band-Pass Transformation . . . . . . . . . . . . . 193.2.4 Lumped to Coupled-Line Transformations . . . . . . . . . . . 203.2.5 Coupled-Line to Hairpin Configuration/ Planar Circuit Design 233.2.6 Designed Layout . . . . . . . . . . . . . . . . . . . . . . . . . 24

4 Results 25

5 Conclusion 26Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

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Chapter 1

Introduction

1.1 IntroductionA band-pass filter is an electronic device that allows signals between two specificfrequencies to pass through, and discriminates any unwanted signals out of thedesired frequencies. The Advance of telecommunication system has enhanced theneed 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 compactsize, high quality in performance together with a low cost is required. Since filter isthe 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 mi-crowave applications. Filters are realized using lumped or distributed circuit ele-ments. However with the advent of advanced materials and new fabrication tech-niques, microstrip filters have become very attractive for microwave applicationsbecause of their small size, low cost and better performance. There are varioustopologies to implement microstrip band-pass filters such as end-coupled, parallelcoupled, hairpin, inter-digital and combline filters. This project represents the de-sign of a hairpin microstrip band-pass filter.

The hairpin resonator filter is one of the most popular microstrip filter configu-rations used in the lower microwave frequencies. It is easy to manufacture becauseit has open-circuited ends that require no grounding. Its form is derived from theedge-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 sig-nificantly as compared to that of the edge-coupled configuration. There are manysubstrates with various dielectric constants that are used in wireless applications.Those with high dielectric constants are more suitable for lower frequency applica-tions in order to help minimize the size [1]. In order to increase the band-width ofend-coupled microstrip band-pass filter parallel coupled microstrip band-pass filter(PCM-BPF) is considered and resonators are positioned so that adjacent resonatorsare parallel to each other along half of their length. This parallel arrangement givesrelatively large coupling for a given spacing between resonators [2]. But this newconfiguration was too long considering the frequency and the order of the filter. Tosolve this problem hairpin-line filter is developed.

Digital broadcasting is a set of transmission standards that aim to broadcast

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signals in digital form with a specific slant. The mode of distributions can be througha medium of satellite, terrestrial or cables. Recently, many countries worldwide aremoving towards a revolutionary change to digital broadcasting. The digital signalbroadcasting 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 andall components will be connected together to accomplish our job, we can find belowthe 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 isthe fundamental component that contributes the overall performance of a commu-nication system.

1.2 ObjectivesThe objectives of this project are:-

1. To design and simulation hairpin band-pass filter at 2.40 GHz operatingfrequency, 5th order Chebychev 0.5 dB ripple and 200 MHz of bandwidth usingADS simulation software.

2. To fabricate and measurement the microstrip filter fabricated on the RogersRO4003c with thickness of 32 mil by using etching technique.

3. To compare between simulation and measurement result.

1.3 Prior to workNowadays filters in the market are more complex. The hairpin filter is better thanother filters because it is compact and does not require grounding. This filter alsoproduces high frequency a wide band filter and comparatively low cost.

1.4 Project MethodologyIn order to design, built and measure the 5th order chebychev band-pass filter inhairpin 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.

2. Calculation, Analysis and Simulation

• Analyzed and calculated all parameters that related to design the stepimpedance hairpin resonance.

• Using ADS software to observe the frequency and scattering response forhairpin filter.

3. Hardware Development and Implementation

• Then proceed to designing microstrip filter using etching technique andmeasure using spectrum analyzed.

• Lastly, compare between simulation and measurement results.

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1.4.1 Filter SpecificationsThe filter is specified as follows:

Parameter Symbol Value Unit Tolerance RemarksFrequency Band f 2.35-2.45 GHz

Bandwidth BW 200 MHz 0.5dB BandwidthType 5 order Chebychev 0.5dB Ripple

Insertion Loss IL 3 dB max in Pass BandReturn Loss RL 12 dB min in Pass Band

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Chapter 2

Theoretical Background

2.1 Background StudyThe use of microstrip in the design of microwave components and integrated circuitshas gained tremendous popularity since the last decades because microstrips can op-erate in a wide range of frequencies. Furthermore, microstrip is lightweight, easierfabrication and integration, and cost effective. Many researchers have presented nu-merous equations for the analysis and synthesis of microstrip. However, along withthe sophistication comes with a high price tag, copy protection schemes and trainingrequirements that create difficulties for exploratory usage in an academic environ-ment. Therefore, a low cost, user-friendly, open source system software package isneeded that can be used as an effective training aid on microstrip filters design.

2.2 FilterA microwave filter is a two-port network used to control the frequency response at acertain point in a microwave system by providing transmission at frequencies withinthe pass-band of the filter and attenuation in the stop-band of the filter [6].

Filters may be classified in a number of ways. An example of one such clas-sification is reflective versus dissipative. In a reflective filter, signal rejection isachieved by reflection the incident power, while in a dissipative filters are used inmost applications. The most conventional description of a filter is by its frequencycharacteristic such as low-pass, high-pass, band-pass or band-reject (notch).

2.2.1 Basic Filter TypesIn microwave communications, there are mainly five types of filter are used whichare briefly described in the following [4]:

2.2.1.1 Low-Pass Filter

Low-pass filter networks transmit all signals between DC and some upper limit wc,and attenuate all signals with frequencies above wc. They are realized by using acascade of series inductors and shunt capacitors. The frequency range of the filter

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specification has been divided into three areas. The passband extends from zerofrequency (dc) to the passband edge frequency fpass, and the stop-band extendsfrom the stop-band edge frequency fstop to infinity. These two bands are separatedby the transition band that extends from fpass to fstop.

2.2.1.2 High-Pass Filter

High-pass filter pass all signals with frequencies above the cut-off value wc to theload with minimum loss and reject signal with frequencies below wc. High-pass filternetworks are realized by using a cascade of series capacitors and shunt inductors.In this case the passband extends from fpass to infinity and is located at a higherfrequency than the stop-band which extends from zero to fstop. High-pass filters areused when it is important to eliminate low frequencies from a signal.

2.2.1.3 Band-Pass Filter

The band-pass filter shows the signal is transferred to the load in a band of frequen-cies 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, definedby the geometric mean of wc1 and wc2[3]. A band-pass filter will pass a band offrequencies while attenuating frequencies above or below that band. In this case thepassband exists between the lower passband edge frequency fpass1 and the upperpassband edge frequency fpass2. A band-pass filter has two stop-bands. The lowerstop-band extends from zero to fstop1, while the upper stop-band extends from fstop2to infinity .

2.2.1.4 Band-Reject (Stop) Filter

The band-reject filter is a complement of the band-pass filter. The signal experienceshigh loss between wc1to wc2, hence the name band-stop or band-reject. In this casethe band of frequencies being rejected is located between the two pass-bands. Thestop-band exists between the lower stop-band edge frequency fstop1 and the upperstop-band edge frequency fstop2. The band-stop filter has two pass-bands, the lowerpassband extends from zero to fpass1, while the upper passband extends from fpass2to infinity .

2.2.1.5 All-Pass Filter

The all-pass filter allows the signal amplitude for all frequencies to pass through thenetwork without any significant loss. This network has no frequency selective passband or stop band.

Typically frequency and amplitude responses for these difference types are shownin figure-3. In additional, an ideal filter displays zero insertion loss, constant groupdelay over the desire pass-band and infinite rejection elsewhere. However, in practi-cal filters deviate from these characteristics and the parameters in the introductionabove 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/Magnitude_Response_Basic.html)

The cut-off frequency is typically defined as the frequency at which the powertransmitted by the filter drops to one-half (by -3 dB) of the maximum power trans-mitted in the passband.

2.2.2 Applications of FiltersAs mentioned above, virtually all microwave receivers, transmitters and so fifth re-quired filters. Typically commonly used circuits that require filters include mixers,transmitters, multiplexers and the like. Multiplexers are essential for channelizedreceivers. Therefore, system application of filters include radar, communications,surveillance, EMS receiver, Satellite Communication (SATCOM), mobile communi-cations, direct broadcast, satellite systems, personal communication system (PCS)and microwave FM multiplexer. In many instances, such as PCS, miniature filter area key to realizing require reduction in size. There is, however, a significant reductionin power handling capacity and an increase in the insertion loss. The former is nota severe limitation in such system, however, and the latter can be compensated forby subsequent power application.

2.2.3 Classifications by Response TypeBased on designing signal processing filters, there are several important classes offilter such as Butterworth filter, Chebyshev filter, Elliptic (Cauer) filter, Besselfilter, Gaussian filter, Optimum "L" (Legendre) filter, Linkwitz-Riley filter. It wasoriginally intended to be applied to the design of passive linear analogue filtersbut its results can also be applied to implementations in active filters and digitalfilters. The class of a filter refers to the class of polynomials from which the filteris mathematically derived. The order of the filter is the number of filter elements

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present in the filter’s ladder implementation. Generally speaking, the higher theorder of the filter, the steeper the cut-off transition between passband and stop-band. In the following some of filters are described shortly.In the following some offilters are described shortly.

2.2.3.1 Butterworth Filter

The Butterworth filter has essentially flat amplitude versus frequency response upto the cut-off frequency. Butterworth filters are also known as maximally flat typefilters and have the flattest possible pass-band magnitude response. This class offilters approximates the ideal filter well in the pass band. It has a monotonic decreasein gain with frequency in the cut-off region and a maximally flat response below cut-off. Attenuation is -3 dB at the design cut-off frequency. Attenuation beyond thecut-off frequency is a moderately steep -20 dB/decade/pole. The pulse response ofthe Butterworth filter has moderate overshoot and ringing. The Butterworth filterhas 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 Chebychev Filter

The Chebychev filter, also called the equal ripple filter, gives a shaper cut-off thanthe Butterworth filter in the pass-band. Both Butterworth and Chebychev filtersexhibit large phase shift near the cutoff frequency. This filter response has thesteeper initial rate of attenuation beyond the cut-off frequency than Butterworth.This advantage comes at the penalty of amplitude variation (ripple) in the pass-band. Unlike Butterworth and Bessel response, which have 3 dB attenuation at thecut-off frequency, Chebychev cut-off frequency is defined as the frequency at whichthe response falls below the ripple band. For even-order filters, all ripples are abovethe dc-normalized pass-band gain response, so cut-off is at 0 dB. For odd-orderfilters, all ripple is below the dc-normalized pass-band gain response, so cut-off isat - (ripple) dB. The Chebychev has more ringing in its pulse response than theButterworth - 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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2.2.3.3 Bessel Filter

For application where the phase is important, the Bessel filter, which is minimalphase shift filter, is used even though its cut off characteristic is not very sharp.The Bessel filter provides ideals phase characteristic with an approximately linearphase response up to nearly cut-off frequency. The Bessel filter has a very linerphase response but a fairly gentle skirt slope. Due to its linear phase response, thisfilter 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.

−6

−5

−4

−3

−2

−1

0

Mag

nitu

de (

dB)

10−1

100

101

102

103

−540

−360

−180

0

Pha

se (

deg)

Magnitude and Phase comparison for diffrent types of filter

Frequency (rad/sec)

ButterworthChebyshevBessel

ButterworthChebyshevBessel

Figure-4: Comparison of amplitude response of Butterworth, Chebyshev andBessel filters.

In order to see the difference between different types of filter a matlab code isimplemented where center frequency is 2.4 GHz and for Chebyshev 0.5 dB ripple isconsidered. From the figure-4 we see that ripple for chebyshev filter.

2.3 Microstrip LineAs circuits have been reduced in size with integrated semiconductor electron devices,a transmission structure was required that was compatible with circuit construction

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techniques to provide guided waves over limited distances. This was realized with aplanar 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 low-loss dielectric material. The size of the circuit can be reduced through judicioususe of a dielectric constant some 2-10 times that of free space (or air), with apenalty that the existence of two different dielectric constants (below and above thestrip) makes the circuit difficult to analyze in closed form (and also introduces avariability of propagation velocity with frequency that can be a limitation on someapplications). The advantages of microstrip have been well established, and it is aconvenient form of transmission line structure for probe measurements of voltage,current and waves. Microstrip structures are also used in integrated semiconductorform, directly interconnected in microwave integrated circuits. Microstrip has a verysimple geometric structure the electromagnetic field involved are actually complex.

Figure-5: Single microstrip transmission line (http://qucs.sourceforge.net).

wherel = 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 transmis-sion like waveguide, coaxial cable, strip line etc. and it has also some disadvantagesas 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.

Disadvantages

a) High attenuation.b) Low power.

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2.3.1 Coupled Microstrip LinesWhen two transmission lines are close together, because of the interaction of theelectromagnetic fields of each line, power can be coupled between the lines. Thosecoupled lines are used to construct directional couplers. Generally, in design ofdirectional couplers microstrip and stripline forms are used. Although microstriptransmission lines do not support TEM and named as quasi-TEM, usually they areassumed 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 Z0e and Z0o (evenand odd mode impedances respectively). In the analysis of the directional couplerswe will use also even-odd mode analysis. Coupled microstrip lines are shown infigure-6.

Figure-6: Coupled microstrip line (http://qucs.sourceforge.net).

The equations for the coupled microstrip lines are shown in the below which areused in our project as well.

Z0J1 =√π∆2g1

, (2.1)

Z0Jn = π∆2√gn−1gn

, (2.2)

Z0JN+1 =√

π∆2gNgN+1

, (2.3)

From above equations we can obtaineven and odd mode characteristic impedances.

Z0e = Z0[1 + JZ0 + (JZ0)2], (2.4)

Z0o = Z0[1− JZ0 + (JZ0)2]. (2.5)

where, Z0= 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 Prototype and TransformationsPrototype filters are electronic filter designs that are used as a template to producea modified filter design for a particular application. They are an example of a nondimensionality design from which the desired filter can be scaled or transformed.They are most often seen in regards to electronic filters and especially linear ana-logue passive filters. However, in principle, the method can be applied to any kindof linear filter or signal processing, including mechanical, acoustic and optical fil-ters. Filters are required to operate at many different frequencies, impedances andbandwidths. The utility of a prototype filter comes from the property that all theseother filters can be derived from it by applying a scaling factor to the componentsof the prototype. The filter design need thus only be carried out once in full, withother filters being obtained by simply applying a scaling factor. Especially useful isthe ability to transform from one band form to another. In this case, the transformis more than a simple scale factor. Band form here is meant to indicate the categoryof passband that the filter possesses. The usual band forms are low-pass, high-pass,bandpass and bandstop, but others are possible. In particular, it is possible for afilter to have multiple pass bands. In fact, in some treatments, the bandstop filteris considered to be a type of multiple passband filter having two pass bands. Mostcommonly, the prototype filter is expressed as a low-pass filter, but other techniquesare possible.

For the specific purpose of this project 0.5 dB Chebyshev filter, filter prototypesare considered from the following table:

Table-1: 0.5-dB Chebyshev LC Element Values.

Order Rs g1 g2 g3 g4 g55 1.0 1.8068 1.3025 2.6914 1.3025 1.8068

These prototype values are applicable for 1 rad/sec cut-off frequency and whensource and load impedance are 1 ohms. From these prototypes LC value it is possibleto switch other filters like high-pass, band-pass, band-stop etc.. In order to achievelow-pass filter scaled to 50 ohms and specific cut-off frequency then below theseequations are necessary.

L′ = R0L

ωc

, (2.6)

C′ = C

R0ωc

. (2.7)

2.4.1 Low-Pass to Band-Pass TransformationIn order to convert low-pass filter to band-pass filter numbers of two conditions aremaintained.

• 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,

L′ = R0L

ωcBW, (2.8)

C′ = BW

R0Lωc

. (2.9)

And for C,

L′ = R0BW

ωcC, (2.10)

C′ = C

R0BWωc

. (2.11)

where, BW is the relative bandwidth.

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Chapter 3

Practical Procedures

3.1 Scope of the workOur main goal is to design a 5th order Chebyshev band-pass filter in hairpin config-uration with a cut-off frequency of 2.4 GHz, 0.5dB ripple and an impedance of 50for both source and load.

3.2 Design ProceduresIn order to design the filter with the specifications mentioned above, the followingprocedures 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 difficultieswhile the implementation.

3.2.1 Low-pass prototype design with lumped elementsUsing table-1, low-pass prototype filter is designed where the cut-off frequency is 1rad/sec. For this design source and load impedances are 1 ohm. This is applicablefor the 5th order low-pass Chebyshev filter with 0.5 dB ripple. Designed circuit canbe 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 herewe are interested to perform simulation for scattering parameters. After runningthe 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 gettingsame response in the figure-8. For 160 mHz cut-off frequency we obtain value ofS(1,1) is -2.701 dB. we can also see the equal ripple in the beginning for S(1,1).

3.2.2 Impedance and Frequency TransformationsBy using the impedance and frequency transformation equations no. 2.6 and 2.7mentioned in chapter 2. Therefore, new values of the L-C elements of the low-pass 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 samedesign structure of the low-pass prototype. Table with the new parameters valuesare shown below.

Table-2: New values after impedance and frequency transformation.

Order C1 L1 C2 L2 C35 1.8068 1.3025 2.6914 1.3025 1.8068C1′

L1′C2′

L2′C3′

R02.398 pF 4.322 nH 3.57 pF 4.322 nH 2.398 pF 50 Ω

After assigned new parameters value our low-pass filter look like in the belowcircuit.

Figure-9: Lumped low-pass 5th order Chebyshev filter.

After performing simulation we see the same response like before and for cut-offfrequency 2.4 GHz we obtain value of S(1,1) is -2.99 dB. We see the effect of responsein the figure below.

Figure-10: Lumped low-pass frequency response.

Simulations are performed for frequency range 0 to 10 GHz. We observe that themarker on the graph indicates the intersection of the S11 and S12 which representsthe value of the cut-off frequency. It can be seen that the cut-off frequency is 2.4GHz as required.

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3.2.3 Low-Pass to Band-Pass TransformationThe low-pass to band-pass transformation illustrated in figure-6 and we can see thatC elements become parallel resonators and L elements become series resonators. Byusing equations no. 2.8, 2.9, 2.10 and 2.11 we achieved lumped elements for 5thorder Chebyschev band-pass filter. Values of lumped elements can be found in thebelow table as well as circuit diagram.

Table-3: Elements value of 5th order band-pass filter.

C1(pF) L1(nH) C2(pF) L2(nH) C3(pF)28.7894 0.153 0.0849 51.885 42.885L3(nH) C4(pF) L4(nH) C5(pF) L5(nH)0.1027 0.0849 51.885 28.7894 0.153

From the above table we see value C1=C5, L1=L5, C2=C4 and L2=L5. Herewe 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 simu-lations we see the nice response for designed band-pass filter. In order to see thebandwidth 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 Lumped to Coupled-Line TransformationsWe know for microwave circuits, lumped elements do not work properly. Therefore,instead of using lumped element it is replaced by coupled or parallel transmissionline for parallel resonators. For the first step we consider ideal transmission linethen we shifted to misrostrip line where we use l/4 transmission lines. So, by usingequations no. 2.1 to 2.5 we obtain the values of coupled transmission lines whichcan be found from the table below.

Table-4: Elements Value of coupled-transmission lines.

n gn Z0Jn Z0e (ohms) Z0o (ohms)1 1.8068 0.2690 67.0681 40.16812 1.3025 0.08525 54.6259 46.10093 2.6914 0.0699 53.7393 46.74934 1.3025 0.06985 53.7393 46.74935 1.8068 0.08525 54.6259 46.10096 1.8068 0.08525 67.0681 40.1681

After getting required values of even and odd impedance for coupled transmissionline 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 transmis-sion line. We marked the positions too see the values of scattering responses and for2.3 GHz we get -2.921 dB and for 2.5 GHz it is -2.428 dB of S(1,1) which is quitereasonable. These responses can be seen in the below figure.

Figure-14: Filter response for band-pass filter with using ideal transmission lines.

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3.2.4.1 Ideal line to Microstrip line transformations

In order to implement filter we know in reality ideal filters doesn’t exist so, we needto convert ideal line to microstrip line. Therefore, to achieve required parameterswhich are applicable for microstrip line we use line calculator tool from ADS softwarewhich is shown in the table below.

Table-5: Required parameters value of microstrip line.

Z0e (ohms) Z0o (ohms) W (mm) S (mm) L (mm)67.0681 40.1681 1.53 0.35 18.354.6259 46.1009 1.7 1.3 18.653.7393 46.7493 1.8 1.4 18.3253.7393 46.7493 1.8 1.4 18.3254.6259 46.1009 1.7 1.3 18.667.0681 40.1681 1.53 0.35 18.3

At first we used MCLIN and we seen that our required bandwidth was reducedafter 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’sreasonable. For this case we marked the positions and also performed momentumto see the magnitudes and phases for every scattering parameters, these responsesare shown in the below. In the below figure-16 we see band width still 200 MHzwhich 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 weobserve the scattering parameters and losses. Simulation result for momentum isperformed 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 ofscattering parameters for both magnitudes and phases. As shown clearly from theresponses, we still have the required filter response.

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3.2.5 Coupled-Line to Hairpin Configuration/ Planar Cir-cuit Design

Our ultimate goal to design 5th order band-pass filter in hairpin configuration so, weneed to convert coupled-line configuration to hairpin configuration. The advantagesof hairpin filter are discussed earlier. For manufacturing and fabrication purposestogether with technical advantages, the planar circuit design is used. In his step,we will design the planar circuit by transforming into planar microstrip lines withports are connected at the end. Using transmission line tool, the parameters of themicrostrip line (width and length) are calculated given the characteristic impedanceand the dielectric constant ( εr= 3.55 ) for our material. The T-junction is used forfabrication purpose and design as follows.

Figure-18: Planar design circuit in hairpin configuration.

After performing simulation for the first time we observed that our frequencyresponse unlikely shifted. So, we varied the lengths in the schematic hairpin filterdesign until we get our desired filter response using tuning option. After that wehave the quite nice response for our band-pass filter and we marked the positionsfor 2.3 GHz and 2.5 GHZ. For these frequency points we get values of S(1,1) -2.167dB and -3.193 dB respectively. It can be seen that some of the microstrip lineshave widths less than 0.05 mm which is not accepted in our design since the etchingmachine will be used for manufacturing the circuit can deal with lines with widthsnot less than 0.05 mm. So, the widths of these lines should be increased, no specificmethods will be used for this, just “try and error”! such that we should still havethe “same” performance. After observing the circuit simulation we get still 0.5 dBripple which is marked by m1.

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Figure-19: Filter response in hairpin configuration.

3.2.6 Designed LayoutIn order to manufacture our designed filter we have generated filter layout. Wehave generated layout for coupled-line configuration and hairpin configuration. Weobserve that our designed layout is most likely similar what we expected which asfollows.

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 andmanufacturing, in the above layout is created. We also see the 3D view of ourdesigned 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-passfilter now we have the hardware view which as follows. We measured our filter withVector 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 man-ufactured view of our designed microstrip band pass filter in hair configuration andsimulation result which is taken from Vector Network Analyzer (VNA). In orderto have test and result we see from VNA our resonant frequency is shifted but weare satisfied because we get nice response for chebychev band pass filter and we aregetting some kind of loss for measuring S12 and S21 due to lossy device. In orderto manufacture this device we see our manufactured device is connected with twocoupled microstrip line which was unexpected, for this reason we disconnected toeach other to have better performance. After the board was milled to the desiredpattern, connectors were attached and the filter was measured using Rohde andSchwarz network analyzer. Figure-22 (b) is the through performance (S21) and re-turn loss (S11) of the prototype filter. The measurements show very good agreementwith 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-offfrequency of 2.4 GHz is designed, fabricated and tested. The circuit is designedusing distributed elements and then planar microstrip lines are used.We have seenthe coupled-line band-pass filter and hairpin band-pass filter respectively. The de-tailed steps are shown, discussed and analyzed. The performance of the circuit isdiscussed basing on the simulations performed for the response of the design. Weget nice results after that if we give more time on this circuit output would morebetter than before. The filter was designed using ADS software with a resultinglayout shown in above figures. This is the familiar hairpin configuration consist-ing of microstrip circuit RF components such as microstrip lines, TEE- sectionsand coupled lines. To perform optimization runs geometrical parameters were as-signed to the individual RF-components. This project reports hairpin filters withimproved characteristics over conventional structures using standard design equa-tions. The line widths and spacing can be easily etched using standard fabricationtechniques. Narrower bandwidths have been achieved without additional compo-nents. The structures are validated having close match between the simulated andpractical results. This approach can be extended to much higher frequency rangewithout compromising the filter performance. Although we don’t get appropriateoutput 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 ADSsimulation software and fabrication technique. In our case we used Rogers RO4003substrate with dielectric constant 3.55 and 32 mil of thickness to fabricate our filterby using etching process.

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Bibliography

[1] S. Peik, Lecture Notes “Microwave Filter Design”, 2009.

[2] D. Pozar, “Microwave Engineering”, second edition.

[3] “Electronic Filter Design Handbook”

[4] Noyan Kinayman, M. I. Aksun,“Modern Microwave Circuits”

[5] Ian Hunter,”Theory and Design of Microwave Filters”

[6] Les Thede,”Practical Analog and Digital Filter Design”,Artech House, Inc. 2004

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