Computing metallic losses for coplanar waveguide | HFSS

Hello everybody,

I have been trying to simulate the design of a CPW using HFSS and I would like to analyse a little bit more the losses mechanisms in the simulation. For that I have been trying to compute the losses due to the finite conductivity of my metallic electrodes (defined as volumetric objects and allowing the solver to solve inside of these objects as well), but so far I have not been able to get the values of these losses as a function of frequency.

I have tried using the field calculator tool, but regardless of the frequency of choise; the obtained losses value is always the same. (I assume that it always returns the value for the expression defined at the last frequency point of computation)

How could I integrate this function into the sweep module of the analysis and finally being able to compute the conduction losses at each one of the different frequency points of evaluation?

Or if anyone has a better idea on how could I compute these losses, it would be also great.

Thanks!

Welcome kalosu,

That should definitely be possible. Can you elaborate on how you are determining the losses?

Hi PlanarMetamaterials,

Thanks for your feedbak.

I would like to compute the losses due to the finite metallic conductivy. I was thinking about using the product of the volume current density with the electric field to compute these losses. I found that one can do this using the field calculator tool, but once one has already performed the simulations.

I would like to run the field calculator tool, but after every invididual frequency point has been evaluated. Allowing me in this way to compute the desired quantity at once and obtain the frequency dependent characteristics of the conduction losses.

I have search online how to do this but so far I have not obtained any helpful information. Do you have any idea about how could I implement this either the field calculator tool or in any other possible manner?

Thanks for your comments and feedback!

You can easily obtain the per-unit-length resistance for the transmission line by taking the port's propagation constant (gamma) and multiplying it by port impedance (Zo) to get the per-unit-length admittance. The resistively of the line is the real part of this. Alternatively, you can get the decay constant (alpha) as simply the real part of gamma, but this includes other losses such as dielectric loss.

Both gamma and Zo are solved for you by HFSS. Just make sure you've selected your frequency sweep when plotting.

Thanks PlanarMetamaterials for your suggestion.

I have tried your suggestion and I noticed that the "resistivity" of the line increases as a function of frequency. Originally; I was trying to obtain from the simulation information, the CPW guided mode losses due to my coplanar waveguide electrodes. As you mentioned the real part of the propagation constant represents the total modal losses, but as said I would like to know more about the portion of the losses due to the finite metallic conductivity.

Would it be possible to extract in some way the total current from the volume current density corresponding to the volumetric sections used for my electrodes? (By this I mean to get the value for each one of the different frequency points evaluated during the sweep)

This is the per-unit-length resistance of the CPW; which will of course be frequency-dependent due to the skin effect. Perhaps you're looking for a different quantity, e.g., at DC?

Edit: I just realized I mistakenly said "admittance" in my previous post; I should have of course said "impedance".

I find it's easier to get total current from the H-field -- draw a loop around the CPW strip and integrate tangential H.

One trivial solution might be to compare DUT losses with/without metal loss included in simulation. For DUT losses, I use loss measure 1 - (|S11|² +|S21|²)

Thanks PlanarMetamaterials and volker@muehlhaus,

Your suggestions were really helpful.

I was able to get the losses contribution due to the metallic electrodes using your recommendations.

Thanks!