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Click here to see PolyStrata coax analyzed with an Henrik Forstén's on-line EM tool
Click here to see PolyStrata 10dB coupler design using Henrik Forstén's on-line EM tool
Click here to see a GaAs microstrip10dB coupler analysed with Henrik Forstén's tool
New for March 2026. An awesome EM tool appears on the Henrik Forstén's website, among a lot of other cool blog posts. Thanks to Alex for pointing this out.
Here is his bio from the site:
My name is Henrik Forstén and I'm a Finnish electrical engineer working as a researcher at VTT. Lately I have focused on mm-wave MIMO radars. I do MMIC design, antenna design, analog and digital PCB design, FPGA programming and PC programming.
His 2D solver can be found here, you should bookmark it:
https://hforsten.com/field_solver.html
This is a great news for those of us without access to expensive EM tools. You can solve microstrip, stripline and GCPW geometries in single and differential modes. Options include solder mask, side walls, ground cutouts and more. Using sidewalls, you can even analyze rectangular coax, a.k.a. PolyStrata coax!
A 2D solver may be a big step up from spreadsheet and linear models (looking at you, Microwave Office), and it is very fast. Did we mention it is free to use!
How it works
In Henrik's own words...
The solver solves static electric field using Laplace's equation. This works for TEM where electric field does not change as function of frequency (until higher order modes). However, for quasi-TEM such as microstrip E-field does change slightly vs frequency which this solver can't capture.
In practice, the dispersion of microstrip at high frequencies which causes the rise in effective permittivity is not modeled correctly. Correctly modeling it would require a different more complicated solver.
2D solver limitations
In practice, you can expect different results using Henrik's solver compared to linear solvers for non-TEM media like microstrip. For the most accurate analyses you should use a 2.5D tools (such as Momentum or Axiem) or 3D tools (HFSS, CST).
2D solvers only work on straight, uniform transmission lines, if you want to analyze bends and other details you will have to find another way to do this.
Microstrip example
Below, we provide a microstrip example...
This is the "Geometry" tab where you set up the all dimensions and material properties except the length of the line (we don't expect you to be able to read the data on this image. One of the fearure of the tool is that you can store your work, including geometry, material properties and analysis frequencies. The data for this example iis stored here so you can go there and run it yourself. When you hit "solve" it draws in the field lines. We like to beat the crap out of tools when we unbox them so we specified 10,000 points. The solution only took about a minute!
The "Results" tab plots the characteristic impedance. We tested it by solving down to 1 MHz. The solver does a nice job of showing low frequency effect on impedance, but it does not report any frequency dispersion.
You can change the X axis to log(frequency). This gives a much prettier image of Z0 over frequency.
The "S-parameter" tab plots S11 and S21 magnitudes. The default length is 1mm, but in this window you can change the length.. This plot represents a 1mm line.
Here is 100mm line. It uses the field solution that was already done, so length changes update the S-parameters almost instantaneously.
By tweaking the metal and dielectric properties you will be able to predict transmission line attenuation. If you really want to predict attenuation accurately you need to fabricate and test sample transmission lines to backfit metal conductivity and dielectric loss tangent, particularly if you plate the transmission lines. Don't be surprised when you observe more loss than you predicted when you use manufacturer's data. 100mm is probably a good length for extracting these parameters at test.
From the S-parameter tab you can download an S2P file.
This is beautiful on-line tool, thanks to Henrik! Now you can move on and admire some more examples
Click here to see PolyStrata coax analyzed with an Henrik Forstén's on-line EM tool
Click here to see PolyStrata 10dB coupler design using Henrik Forstén's on-line EM tool
Click here to see a GaAs microstrip10dB coupler analysed with Henrik Forstén's tool