How to obtain the proper S-parameter values for low pass filter Richard's method

Dear Sir,

I tried for the Richard's transformation method lowpass filter design , got the proper s-parameter values for the schematic simulation. But I didn't get expected s-parameter values for the EM extraction. Design values are as follows.

Z0= 50 Ohm, f = 4 GHz, H=1.6mm , T =0.036, dielectric constant =4.4, Tangential loss =0.001

I am expecting following values for both SCHEMATIC and EM Extraction


Frequency DB S(1,1) DB S(2,1)

4GHz -3.1084 -3.0946
Herewith I am attaching the present getting layout and schematic diagram. Can u help anybody to get expected s-parameter values

Check the cell size for your EM extraction. From what I can see, the cell size defined in the extraction block is much bigger than the width of the narrow lines.

Some other hints: you can not make the high impedance transmission lines so narrow that they are very lossy and expect the performance to look like the lumped element prototype. ALso, the richards transform is a narrowband thing....you have to decide what frequency (i.e. what stub lengths) you want the transmission line model to best match the lumped model. For a lpf, I usually make the two match as closely as possible at the cuttoff frequency Fc of the lpf.

Volker Sir,

I changed the cell sizes to 0.01mm for both x & y cell size , am getting error. Even I changed the MWO simulator like ,OEA, ACE, VELOCE RF and AXIAM, for those simulator also getting the error sir.

It is difficult to help if we don't know what error you get. Certainly, a small cell size will require additional memory. But if you have these ultra narrow lines, you need to set the cell size small enough to mesh the narrow lines.

But anyway - as biff44 wrote, the <10μm line width is a problem anyway. Redesign your filter with a wider line (maybe 50μm or more) that can realistically be manufactured.

VOLKER Sir,

It is showing the following errors sir,

1. Not enough memory to creat moment tables
2. An error occured in the remote em simulator "EM Sight " fatal error
3. EX1 unable to simulate the circuit refered by the model
4. unable to enumerate the circuit
5.An error occured in the simulator while processing EM EXTRACT_DOC.SFDOC

Ok, makes sense. This is because the mesh with small cell size is more complex -> needs more memory. But if you simulate with 0.1mm cell size, all lines will be simulated with n*0.1mm width. The narrow lines from your schematic will be EM-simulated with 1 cell = 100μm width. This is a big difference from the line width that you defined in the schematic.

If you can not use a smaller cell size in EM, then you should re-design for wider line width.