Antenna Toolbox simulations come out wrong

Question

Joshua 2025-2-24

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https://ww2.mathworks.cn/matlabcentral/answers/2174422-antenna-toolbox-simulations-come-out-wrong

回答： Mike Croucher 2025-3-19

I did the following with the Antenna Designer from the Antenna Toolbox:

Open Antenna Designer App
Click "New"
Choose "Monopole" from the "Antenna Gallery"
Enter "Design Frequency" of 10 MHz
Click "Accept"
Set "GroundPlaneLength" and "GroundPlaneWidth" to "Inf"
Set "Width" to 0.01
Click "Apply"
Click "Impedance" under "Vector Frequency Analysis"

Here's the model displayed in the designer:

And I observe that the resistance at resonance (where reactance is 0) is about 22 ohms. This is really far off from a proper calculation of a quarter wave monopole over a perfect, infinite ground plane.

If you use 4NEC, MMANA, etc., you'll find that the resistance will come out to about 36 ohms. And if you build a real quarter wave monopole over a large, flat ground plane, you'll measure approximately the same with a VNA. Here's an example simulation of the same antenna in MMANA:

What am I doing wrong? I have trouble thinking that the Antenna toolbox would be so wrong on such a fundamentally simple antenna model... so I assume I'm not doing something correctly. The documentation doesn't seem to add any extra help, so I hope I can find someone to give me a nudge in the right direction!