drkirkby
Full Member level 6
I tried to create a loop antenna, consisting of a single closed loop for 144.3 MHz. I wanted to set the diameter so the real part of the input impedance was 50 Ohms, and then tune out the inductive part with a capacitor. So I set up this HFSS model, and found a radius for the loop where the input Z is 50 + j X Ω. So I built the loop according to those dimensions. When I measure this on a VNA, I am seeing 119 + j 138. Ω
I've tried converging on both the usual delta S of 0.02, as well as setting up expressions for R and X, and converging on them. Whatever I do, this is sufficiently far from measurements to alert me something is wrong.
For the measurements an N connector was put directly across the loop. After calibrating with an N calibration kit, I applied a small port extension to move the reference plane to the loop. I did this by putting a short across the loop, and adjusting for a phase of 180 degrees. At this frequency (wavelength around 2 m), the N connector is pretty insignificant.
The feed cable was taken out horizontally. I don't know if the fact the computer model does not include the feed is the problem. I could simulate with a waveport and include some coax in it. Also there is no balun. These might be the cause of the problem, or it might just be the model is very wrong.
Dave
I've tried converging on both the usual delta S of 0.02, as well as setting up expressions for R and X, and converging on them. Whatever I do, this is sufficiently far from measurements to alert me something is wrong.
For the measurements an N connector was put directly across the loop. After calibrating with an N calibration kit, I applied a small port extension to move the reference plane to the loop. I did this by putting a short across the loop, and adjusting for a phase of 180 degrees. At this frequency (wavelength around 2 m), the N connector is pretty insignificant.
The feed cable was taken out horizontally. I don't know if the fact the computer model does not include the feed is the problem. I could simulate with a waveport and include some coax in it. Also there is no balun. These might be the cause of the problem, or it might just be the model is very wrong.
Dave