Coupled line filter design

Hi all,

can anybody explain how coupled line filter works..., simple derivation will be appreciable in terms of even and odd mode .

In all MMIC foundry PDKs, they are supplying coupled line models,how much tight coupling can be achieved while fabricating a coupled line filter in GaAs substrate.

Please help me.

Appuarpita

It's a complicated subject.You'd better read some textbooks on them.

there are half wave resonators. Those have a bandpass filter characteristic. By controlling the effective characteristic impedance of the various resonators, and by controlling the coupling in and out of each resonator, you can approximate a bandpass of a desired bandwidth and rejection.

The Square root of Even times Odd mode impedance is a little like a characteristic impedance of a transmission line. The DIFFERENCE of even minus odd mode impedance is kind of like a coupling factor level.

other than that, you have to consult the old research papers.

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you want to read Matthaei Young and Jones, page 473

Just keep in mind that many of the closed form equations for these filters are based on TEM structures (Striplilne, slabline, etc). Microstrip is NOT TEM mode, so the even mode and odd mode energy propagates at slightly DIFFERENT phase velocities...meaning you need to trim the lengths in microstrip using the correct even and odd mode effective dielectric constants.