report on microstrip 09-01-2013

8/12/2019 Report on Microstrip 09-01-2013

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Design 1: Design of conventional hairpin filter

Hairpin line filters are compact structures. By folding the parallel coupled half

wavelength resonators into u shape hairpin resonator is obtained. To allow for bending a sliding factor is

introduced. This makes the

design compact.

Consider an example: A band pass filter is designed to have a fractional bandwidth

of .!" at a centre fre#uency of

!.$ %H&. A $ pole chebyshev low pass prototype with a pass band ripple of .' db

is used. The element

values are g (g)('. * g'(g$('.'+)"* g!(g+( '.,-'! and g,('. -$ . These low

pass element values are used

to determine the design parameters of band pass filters such as coupling coefficient

and external #uality

factor. The band pass filter parameters can be calculated by

/e'(g g'01B2

/en(gn gn3'01B2

4i5 ( 1B20gigi3' for i( ' to n6'

2here 4 i53' are the coupling coefficients between the ad5acent resonators and / e' and / en are the external

#uality factors at the input and output.


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Fig: 7ayout of conventional $ pole microstrip 1ig: 8imulated response of Bandpass filter conventional B.9.1

The low pass prototype element values and 1B2 are substituted in to the e#uations '; < ,; to obtain

the design parameters for the filter. The results are

/ e' (/ e$(+. $-

4 '! (4 +$( .!!,

4 !, (4 ,+ ( .'-

The overall response of the band pass filter is determined by the coupling between the resonators. 8o the

coupling coefficient is related to the spacing between the resonators. The coupling coefficient can be

varied by varying the spacing between the resonators by using the formula

=( f ! ! 6f ' ! ;0 f ! !3f ' !;

The spacing for the re#uired #uality factor can be determined by using the above formula where f ' and f !are the two peak resonances. These resonance fre#uencies are obtained from the simulated response 8 !'

for two resonators.

The band pass filter is designed to have tapped line input and output. The tap distance affects the overall

bandwidth performance of the filter and therefore the #uality factor is affected. The tapping location t is

obtained as )mm. The characteristic impedance of the tapped line is obtained such that it matches to the

$ > terminating impedance. 1or the proposed filter characteristic impedance of tapped line is )".+> and

the width is '."mm.

Different methodology adapted for Desigining Hairpin microstrip bandpass

filter

'. ?esign of Hairpin Band 9ass 1ilters for 86Band Application


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4icrostrip filters play an important role in many @1 applications. As technologies advances*more stringent re#uirements of filters are re#uired. ne of the re#uirements is the compactnessof filters. Bandpass filters are essential building blocks for communication systems. They canreduce the harmonic and spurious emissions for transmitters* and may improve the re5ection ofinterferences for receivers. To ensure an easy integration between band pass filters and other

active devices* many previous works on designing planar filter were reported. Among varioustypes of planar filters* the parallel6coupled band pass filter based on half6wavelength* 0!resonators exhibits the merits of simple synthesis procedure* good repetition* and a wider rangeof reali&able fraction in bandwidth. However* the conventional microstrip parallel coupled band

pass filter suffers from the spurious response at twice the center fre#uency* ! f o* making there5ection of the upper stop band worse than the lower stop band. This was due to une#ual evenand odd mode propagation constants for microstrip coupled6line sections. 4any works have beenreported to overcome this issue by e#uali&ing the effective dielectric constants or electricallengths of the even and odd modes. However* these techni#ues either rely on complexdesign0optimi&ation procedures or limit the filter to specific circuit configurations. 8omemethods that are used the capacitive coupled gap and the 0+ open stubs were adopted in the

circuit to create two transmission &eros* such that the selectivity of parallel coupled band passfilter can be improved. n the other hand* microstrip band pass filters based on 0+ resonatorsmay feature more compact circuit si&e as well as better stopband re5ection with no spuriousresponse at ! f o..

report on microstrip 09-01-2013

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