Some questions about microstrip filter.

Hi pva:
I use ADS to make circuit and EM simulation.
EM engine is Mom MW.

mamali said:

htforever said:

Now I changed my substrate, A substrate for high frequency circuit.
Er=2.8, H=1mm. But I don't know the tanD, is 0.02 OK?

Click to expand...

you should use a resonable substrait, which is available at the market, you may use this:
RT/duroid 6002 ; er=2.94 +/- 0.04; loss tangent: tand= 0.0012 (at 10GHz). but this is an expensive material . dont forget to search for an available substrait, it is very impotant, and you can not gain a practical design, if your substrait is not achievable.

and, the simulation results (MoM is better, especially Zelan d's IE3 D), should be trusted, not the lumped elements models (such as what is available in Micr0wave 0ffice).

marti

Click to expand...

Hi Mamali - I work for AWR, and I disagree with this last statement. We have gotten very good results with these types of filters when comparing the MWO circuit models with EM results (and measured data.) Our circuit models are not just closed form equations, or lumped elements. Our coupled line models are based on EM quasi-static simulations that run when you simulate your circuit, and discontinuities such as MTEE and MLEF are based on EM simulation results specific to the user's substrate.

Of course, a good EM simulator, properly set up, and modeling all enclosure effects, should give you the most accurate answer. But our users have found that starting their designs from our circuit elements gets them very close to the desired result. In fact, if you look in our examples folder you will see filters similar to what htforever posted, comparing circuit to EM to measurement.

dear htforever,
i design this filter for ya, using Zeland's FilterSyn, it is a stepped-impedance microstrip lowpass filter (as you mentioned: er=2.8, H=1mm).


Filter charasteristics:
High Impedance Line width = 0.5mm
Low Impedance Line width = 10mm
#1: Low Z, L=10.50mm
#2: High Z, L= 9.31mm
#3: Low Z, L= 8.78mm
#4: High Z, L=10.19mm
#5: Low Z, L= 8.77mm
#6: High Z, L=11.36mm

here is a schematic of the filter, explaining the above parameters. and, the simulated S11 on 1E3D.

cheers, marti

Hi Marti,

this filter needs a little tuning, the return loss in the passband is poor. You should try to achieve at least 15 dB.

rgds, Al

AL0117 said:

Hi Marti,

this filter needs a little tuning, the return loss in the passband is poor. You should try to achieve at least 15 dB.

rgds, Al

Click to expand...

dear al,
he(htforever) wants a 3db max loss in passband => 3dB return loss. i think this is poor design too, but these are his design specifications. this is the simplest and smallest design i achieved in about 30 mins. better maybe achieved by other friends. .

marti

Hi,mamali:
Thank you very much for your design!
I will consider it.
Thanks for everyone's supporrt.