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Microstrip Coupled line filter design using Rogers Ro4003

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ramin.ala

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Hi everyone

I have designed a coupled-line filter at X-band using Ro-4003 with 8mil of thickness.

Rogers Software (MWI-2016) suggests dielectric constant of 3.81 for this substrate, this thickness, and at X band. this number has significant difference with popular dielectric constant for RF design using RO4003 (I mean 3.55).

What is your suggection? should I use 3.55 in my design (and expect shift in response!) OR use 3.81 and be optimistic!
 

I'd suggest using 3.55 until proven otherwise. When working with a board material that I'm not familiar with, I also make a 50 ohm line to verify my trace width. Sometimes this 50 ohm line can be chopped from the input or output trace and connectorizing this. 4003 is quite common.
 
Recently I asked PCB fabrication house about RO4003 and was surprised by this fact. They have recommended Er values for design (without stating frequency, only thickness) , while still providing standard Er value of RO4003. Why still providing standard value? Is it frequency and thickness dependent value?
 

Er is related (to some extend) on a number of factors. I would expect that John Coonrod @ RogersCorp could do an all day discussion on this topic.
h**ps://www.rogerscorp.com/documents/726/acm/RO4000-Laminates---Data-sheet.pdf
The above data sheet shows Er (Dk) vs Frequency. Design engineers have to start with some number to select substrate and thickness... and keep track of assumptions. I do mostly octave and multi-octave designs.
 

ramin.ala said:
Hi everyone

I have designed a coupled-line filter at X-band using Ro-4003 with 8mil of thickness.

Rogers Software (MWI-2016) suggests dielectric constant of 3.81 for this substrate, this thickness, and at X band. this number has significant difference with popular dielectric constant for RF design using RO4003 (I mean 3.55).

What is your suggection? should I use 3.55 in my design (and expect shift in response!) OR use 3.81 and be optimistic!
Click to expand...

I haven't tried the MWI-2016 version yet, but using MWI-2014 at 10GHz, the software provided a frequency related Er value of approx 3.7 for RO4003 of 12mil thickness and the filter centering was pretty good.
 
edf said:
I haven't tried the MWI-2016 version yet, but using MWI-2014 at 10GHz, the software provided a frequency related Er value of approx 3.7 for RO4003 of 12mil thickness and the filter centering was pretty good.
Click to expand...

Thank you.
This answer is what exactly I looked for (experience with dielectric constant, suggested by MWI).

Another question is about non-isotropic dielectric constant of RO4003 (it shows slightly different dielectric constant in X, Y, and Z directions). Therefore, its dielectric constant may also be depend on structure that is printed on substrate.

Is it correct?

It it possible to define a non-isotropic substrate (as mentioned above) in HFSS (or CST)?
 

ramin.ala said:
Thank you.
This answer is what exactly I looked for (experience with dielectric constant, suggested by MWI).

Another question is about non-isotropic dielectric constant of RO4003 (it shows slightly different dielectric constant in X, Y, and Z directions). Therefore, its dielectric constant may also be depend on structure that is printed on substrate.

Is it correct?

It it possible to define a non-isotropic substrate (as mentioned above) in HFSS (or CST)?
Click to expand...

I've only had trial exposure to HFSS and CST. I did use the Er value from MWI for my full-wave EM simulation in AWR's Microwave Office.
 

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