1. Design of Combline Bandpass Filters
Interdigital BPF included

2. Comline Bandpass Filters
Typical Combline Bandpass Filter

3. Equivalent circuit

4. Coupled section
equivalent circuit
Zoe, Zoo

5. Slope parameter
Use the following resonant condition:

6. Coupling coefficient(1)
J-inverter:
Coupling coefficient:

7. Coupling coefficient(2)
Coupling coefficient inversely proportional to the frequency

8. Combline Bandapss Filter

9. Equivalent circuit for 1st and last stage
Interdigital type feeding

10. Coupling stage
Combline type

11. Equivalent circuit(1)
Equivalent circuit

12. Design equations

15. Equivalent circuit(2)
Reduced circuit

16. Equivalent circuits

17. 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

18. Interdigital Bandpass Filter
Input feeding – shorted
30% bandwidth or less

19. Equivalent circuit

20. Design procedures

21. Design equations

22. Designed Filter

23. Input feeding –Open
30% bandwidth or more

24. Equivalent circuit

25. Design equations(1)

26. Design equations(2)

27. From Filter Specifications

28. Design Example
Open ended feeding
At 2 GHz 10% bandwidth, Order 3

29. Layout of microstrip interdigital BPF
SPEC
Order : 3
FBW : 10%
Center frequency : 2GHz
Resonator width : 모두 같게 설계
Resonator length
Case 1.
Case 2.
Substrate
Dielectric : 6.15
H=1.27mm
TanD :

30. Layout of microstrip interdigital BPF
Step 1
에 따른 resonator length를 구한다.
Step 2
-slope parameter를 정해
even mode addmittance값을 구할 수 있다.(resonator width)
Step 3
-J inverter 값과 even mode addmittance값을 통해 odd mode
addmittance값을 구한다.(resonator들 간의 간격 s)

31. Simulated Results(1)
Center frequency
: 1.952GHz
1dB BW
:210MHz(11%)

32. Simulated Results(2)
Center frequency
: 2.040GHz
1dB BW
:210MHz(11%)