RectWaveGuide Port in PCB Antenna, seem to not work

[domebevi]

Hello everyone,

I have been trying to implement the following example from CST Studio:
#https://www.researchgate.net/publication/333292532_Design_and_Simulation_Microstrip_patch_Antenna_using_CST_Microwave_Studio
in OpenEMS.

I've figured out how to build the PCB model and the mesh (you can find my CSXCAD file attached), but I’m still having trouble with the rectangular waveguide port. In the image, you can see how the author creates it in CST. I’ve used the same measurements in my code, but I’m getting an unusual impedance and, most annoyingly, an empty S11 plot due to the error:

RuntimeWarning: invalid value encountered in divide s11 = port.uf_ref/port.uf_inc

I'm not an expert, so it’s probably my mistake, but could someone please help me figure out how to fix it?

Here’s the port snippet:

a = 7*Wf
b = 5*substrate_thickness + 2*trace_thickness

start=[0 - a/2, -L, 0]
stop =[0 + a/2, -L, b]
mesh.AddLine('z', [start[2], stop[2]])
port = FDTD.AddRectWaveGuidePort( 0, start, stop, 'z', a*unit, b*unit, "TE10", 1)

where Wf is the trace width going to the patch antenna, -L is the edge of the board and starting point of the trace.

You can find the full code file and the geometry file inside the zip file.

Thank you!

xml file + code.zip

[thliebig]

In the (I guess) CST image that is certainly not a rect waveguide port. A also do not see any rect waveguide?
Instead you should just use a simple lumped port at the edge or maybe a MSL port as this is a patch edge feed by a MSL.

[domebevi]

First of all thank you for your answer, I was considering using the lumped port indeed, but how should I place it and how should it be dimensioned? I mean, I know it should be on on the edge of the feed-line (right?), but should it be a 1-D line (z axis) or a rectangular (x length = strip width, z = substrate thickness) ?

[thliebig]

it should be as wide as the MSL and thus a 2D plane from the ground to the MSL.

[domebevi]

thank you!