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microstrip low pass filter

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J0hn

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microstrip low pass filter design

Just wonder beside step impedance and elliptic, is there any topology that is compact enough to design microstrip low pass filter, i trying to make the length of the filter to be less than 15mm.

I had attempt to use Alumina (10 mil thick) as substrate, to do a low pass filter at which the bandpass is up to frequency 4.5GHz, but then the problem is that the inductance line of this kind of filter is very long, and i had try to bend the inductance line in order to make it compact. Beside that i trying to hit a rejection of -50dB at 5.1GHz, in order to do so, i have to increase order, but then these will cause the filter to be very big. I also try to design a bandstop filter in order to meet the rejection, but is too big to be used, so i give up on that idea.

Anyone can advise me how to make the microstrip filter as compact as possible and yet meet the rejection? Thanks.
 

Hi,
I need some advice regarding the RF connectors to the microstrip circuit. I'm a beginner in RF and uWave.
I fabricated a simple microstrip transmission line and connected two SMA connectors using solder. But the result on Network Analyser was far from expected. I think there is something wrong with my soldering. Perhaps the solders result in parasitic capacitance.
So are there any point i need to know while soldering microwave circuits?
 

Hi, John

What bandwidth is real pass band?
If pass band width is narrow, do you try band-pass filter?
For same rejection value band-pass filter is small order than low-pass filter.

There is combline and interdigital filter in band-pass filter.

regards
 

Hi, micro_mory,

The passband is from 0 to 4.5GHz, and i try to design such that the insertion loss will not be greater than 1 dB at the passband. Also i try to avoid via in my design if possible. As the use of via take more time to fabricate out and test the result and quite costly.

Added after 13 minutes:

Hi magnetra,

Perhap, u can check the what is the max frequency the SMA connector that you r using can support to.

And common mistakes, i committed last time is, if you are using coplanar waveguide, check the side, make sure the ground is not short to the connector pin, and for microstrip, sometime i didn't solder the ground of the SMA connector properly, hence affect the result. Also check that there is no gap between the substrate and the connector. It will be easier to use a microscope to check whether there is any problem of the connecting point between the SMA connector and the substrate, sometime i accidently short the grd and the pin, becos of my lousy soldering skill. Maybe is not the connector problem, you can look at other area, maybe is transmission line, or the calibration of the network analyizer. :)
 

Hi,

maybe you can think of mixing lumped and distributed elements? This could be the way to minimize the filter size, you can avoid long inductive lines by replacing them with inductors.

flyhigh
 

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