Design of Combline Bandpass Filters - E-Doodles · Combline Bandpass Filters Interdigital BPF...

Design of Combline Bandpass Filters

Interdigital BPF included

Microwave & Millimeter-wave Lab.

Comline Bandpass Filters

2

Input Output

Typical Combline Bandpass Filter


Equivalent circuit

3

J12 J23 J34

GA

b1 b3Yin

a

J01

b2

GB

Input coupling

Output coupling


Coupled section

equivalent circuit

4

Y2 , l

Y1 , l

Y3 , l

Zoe, Zoo


Slope parameter

5

Use the following resonant condition:


Coupling coefficient(1)

J-inverter:

Coupling coefficient:

6


Coupling coefficient(2)

Coupling coefficient inversely proportional to the frequency

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Combline Bandapss Filter

8


Equivalent circuit for 1st and last stage

Interdigital type feeding

9


Coupling stage

Combline type

10


Equivalent circuit(1)

Equivalent circuit

11


Design equations

12

Microwave & Millimeter-wave Lab. 13


Equivalent circuit(2)

Reduced circuit

15


Equivalent circuits

16


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

17


Interdigital Bandpass Filter

Input feeding – shorted

30% bandwidth or less

18


Equivalent circuit

19

Y2 , lY1 , l Y3 , l

YA

1:N

Y12 , l Y23 , l Y34 , l

……

……


Design procedures

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Design equations

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Designed Filter

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Input feeding –Open

30% bandwidth or more

23


Equivalent circuit

24

J12 J23 J34

YA

b1 b3

J01

b2

YB


Design equations(1)

25


Design equations(2)

26


From Filter Specifications

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Design Example

Open ended feeding At 2 GHz 10% bandwidth, Order 3

28


Layout of microstrip interdigital BPF

29

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 = −


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

====


Simulated Results(1)

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(1 )2 2

FBWπθ = −90oθ =

Center frequency

: 1.952GHz

1dB BW

:210MHz(11%)


Simulated Results(2)

32

(1 )2 2

FBWπθ = −

Center frequency

: 2.040GHz

1dB BW

:210MHz(11%)

Design of Combline Bandpass Filters - E-Doodles · Combline Bandpass Filters Interdigital BPF...

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