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Demo code (matched precision load for Coaxial ports)

Posted: Wed 13 Jan 2021, 19:56
by Tobago

I am posting some code that I developed to construct high precision matched loads for coaxial ports. You are welcome to use it.

FDTD far field simulations of antennas with coaxial feeds require the NF2FF surface to
completely contain the system. Power from a source in a coaxial port flows in both
directions. Power flowing in the unwanted direction must be absorbed. Running the port into
a PML wall is ruled out here by the NF2FF containment requirement. Hence the need for a
matched load in the port with a return loss comparable to PML.

The openEMS AddCoaxialPort function is augmented with a capped disk lossy dielectric load
that achieves high return loss (better than PML ) between 0.5 and 1.5 GHz when calibrated to
the FDTD grid. A calibration routine has been developed. The calibration requires temporary
connection of the open end of the port to PML to allow accurate S11 measurements. Obviously the
grid must not be changed or the load moved without recalibration.

Attached files

LoadCalDemo.m openEMS Octave Demonstration of Load Calibration
AddCoaxialPort2.m : Modified version of openEMS AddCoaxialPort.m
load_model.m mode matching analyzer for the subject load

You run LoadCalDemo.m it calls functions in the other two files.

I will post some of the output plots in another post.
Happy for comments, suggestions etc.

David Slatter (openEMS username Tobago)

PS I have very much enjoyed learning from openEMS. Thank you to Thorsten for sharing it with us.

Re: Demo code (matched precision load for Coaxial ports)

Posted: Wed 13 Jan 2021, 20:17
by Tobago
I forgot to post a picture of the construction of the load. (Very simple)

I also show sample plots from LoadCalDemo,m, The plots are annotated with load size etc.


coaxial port load S11 plot
PS119.jpg (40.11 KiB) Viewed 1496 times


Best Wishes,
David Slatter