design of combline bandpass filters - e-doodles · combline bandpass filters interdigital bpf...
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Microwave & Millimeter-wave Lab.
Comline Bandpass Filters
2
Input Output
Typical Combline Bandpass Filter
Microwave & Millimeter-wave Lab.
Equivalent circuit
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J12 J23 J34
GA
b1 b3Yin
a
J01
b2
GB
Input coupling
Output coupling
Microwave & Millimeter-wave Lab.
Coupling coefficient(2)
Coupling coefficient inversely proportional to the frequency
7
Microwave & Millimeter-wave Lab.
Equivalent circuit for 1st and last stage
Interdigital type feeding
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Microwave & Millimeter-wave Lab.
Interdigital BPF-Introduction
Attractive features Very compact Required tolerances in manufacturing are
relatively relaxed because of the large spacing between resonator elements
The spurious response appears at there times the center frequency of the passband
The rates of cutoff and the strength of the stop bands are enhanced by multiple poles attenuation at dc and at even multiples of the passband center
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Microwave & Millimeter-wave Lab.
Interdigital Bandpass Filter
Input feeding – shorted
30% bandwidth or less
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Microwave & Millimeter-wave Lab.
Equivalent circuit
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Y2 , lY1 , l Y3 , l
YA
1:N
Y12 , l Y23 , l Y34 , l
……
……
Microwave & Millimeter-wave Lab.
Design Example
Open ended feeding At 2 GHz 10% bandwidth, Order 3
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Microwave & Millimeter-wave Lab.
Layout of microstrip interdigital BPF
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SPEC
Order : 3FBW : 10%Center frequency : 2GHzResonator width : 모두 같게 설계
Resonator lengthCase 1.
Case 2.
Substrate
Dielectric : 6.15H=1.27mmTanD : 0.0013
90oθ =
(1 )2 2
FBWπθ = −
Microwave & Millimeter-wave Lab. 30
Step 1- 에 따른 resonator length를 구한다.
Step 2
-slope parameter를 정해even mode addmittance값을 구할 수 있다.(resonator width)
Step 3-J inverter 값과 even mode addmittance값을 통해 odd mode addmittance값을 구한다.(resonator들 간의 간격 s)
θ
Layout of microstrip interdigital BPF
0
1
2
3
4
10.62920.97020.62921
ggggg
=====
01
12
23
34
0.11370.52080.52080.1137
JJJJ
====
Microwave & Millimeter-wave Lab.
Simulated Results(1)
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(1 )2 2
FBWπθ = −90oθ =
Center frequency
: 1.952GHz
1dB BW
:210MHz(11%)