how to design microstrip filter with high stopband rejection

[hanway]

I want to design microstrip bandpass filter at 2GHz, the bandwith is 60MHz, but at the 130MHZ, it require -80dB rejection. I know if waveguide filter maybe meet the requirement, but I don't know whether the microstrip can reach it. anyone have experience can give me some advice
Thanks !

 

[flatulent]

Re: how to design microstrip filter with high stopband rejec

This shape factor (3 dB down bandwidth compared to 80 dB down bandwidth) will take at least an eight resonator filter. One trick would be to use two each four resonator filters separated by a gain stage so they do not interact and so that you can compensate for the insertion losses.

Another advantage of this two step approach is that the ultimate rejection way out of band is increased because the input and output of the complete total filter are much further physically away from each other and the parasitic coupling between them is reduced.

 

[radiohead]

Re: how to design microstrip filter with high stopband rejec

Is it possible to get much better stopband rejection with stripline filters? Can you put a number on that?

 

[hanway]

Re: how to design microstrip filter with high stopband rejec

I design the suspended microstrip filter in order to get higher Q and try to introduce cross coupling to improve outband rejection.
flatulent : you mean design the active filter? i am a fresh man in this, can you give more advice about "gain stage".thanks!

 

[flatulent]

Re: how to design microstrip filter with high stopband rejec

My statement meant to have two passive filters with an ordinary gain stage between. this helps with the noise and distortion performance in some systems if the filter has high insertion loss. The two filters can either be identical with half the ripple you can withstand for the whole filter,or you can split half of the poles for each filter.

 

[harmony]

Re: how to design microstrip filter with high stopband rejec

hello guys,
I ve designed many planar filters in microstrip and suspended stripline tx-lines, my advice if u need a higher rejection is definitely to use suspended stripline, because it has lower losses than microstrip, or equally to use a shielded microstrip line (the idea is simply to reduce the radiation losses caused by the line itself, especially for bandpass coz they are more senstive 2 losses !

Hint: try 2 design a transmission-zero at this frequency 2 achieve ur desired rejection !


goodluck

 

[randyding]

Re: how to design microstrip filter with high stopband rejec

For the microstrip, it is almost impossible to get -80dB rejection. even simulation is good.
suggest use stripline or other type filter.

 

[hanway]

Re: how to design microstrip filter with high stopband rejec

hi all: i try to introduce transmission zeros near the passband to achieve high rejection. but the TZs is so close to the passband , the passband insert loss becomes very bad.
in addition, for resonator, are there any available resonator beside open loop resonator , hairpin ?