I did a simulation of an antenna and replicated the antenna in an experiment however the simulation is coming out to be roughly the opposite. From the experiment I was expecting this plot to spiral from 1420 to 650 clockwise, however it's counterclockwise. enter image description here

I don't have a background in electrical engineering and I was wondering, what could flip the pattern like this? Could it be that my dielectric for the simulation isn't chosen correctly or could it be that the dimensions of the simulation are incorrect? Any help would be greatly appreciated!

EDIT: the measurement was done with a vector network analyzer connected to the antenna with a SMA connector cable on one port. It's a two port system but the other port has a 50 ohm terminator.

  • 1
    \$\begingroup\$ Can you plot your simulation and measured results on the same chart? As it is, I'm not sure what you're asking. The trace on the plot presented appears to go clockwise. \$\endgroup\$
    – The Photon
    Commented Dec 28, 2016 at 19:25
  • \$\begingroup\$ Sorry, spiraling in from 1420 to 650 it should be clockwise, and spiraling outwards from 650 to 1420 it should be counterclockwise. I will try to add both \$\endgroup\$
    – boson
    Commented Dec 28, 2016 at 19:43
  • \$\begingroup\$ Also, a description of how you actually did the measurement and how you accounted for cables between the measurement instrument and the antenna would be helpful. \$\endgroup\$
    – The Photon
    Commented Dec 28, 2016 at 20:09
  • \$\begingroup\$ I'm no RF expert (they're all on the Amateur radio SE), but I was under the impression that inductive reactance spirals one way while capacitive reactance would cause the plot to spiral the other way. The right stub/length of transmission line can flip the sign of the reactive impedance so maybe there's an unaccounted stub somewhere? \$\endgroup\$
    – Sam
    Commented Dec 28, 2016 at 20:10

1 Answer 1


Always refer to clock for increasing frequency and for standing wave impedances on simple antennae , it should be clockwise increasing f over the band of interest.

So it is showing as it should with many standing wave resonance points closest to the centre thru an octave in frequency.

Except your impedance is mismatched and circling around and only achieves perfect Gamma=1 near 0.7GHz.

(for a real measurement), this assumes your cables are calibrated with a fixed R to give a perfect dot at center, which may not be true if using cheap coax instead of semi-rigid copper tubing for the test.


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