understanding and measuring circular polarization
I have a few doubts about measuring circular polarized antennas. One method is measuring the antenna under test (AUT) with a linear polarized reference antenna (RA) in 2 orthogonal planes. That is the RA is rotated 90° and the AUT's pattern is measured. If I want to have a radiation pattern in 2 planes, the result is 4 measurements. Now, how do I combine the results to give the RHCP gain, LHCP gain and axial ratio in the 2 planes of the AUT? In other words, what are the equations? I have both the amplitude and phase of the 4 measurements and the results are calibrated.
Thank you very much.
Best regards.
I know in hardware if you use linear polarization to detect horizontal and vertical, you can combine them with a 90 degree hybrid to get RH and LH circular polarization. It should be easy mathimatically to also do this.
Polarization in Electromagnetic Systems, Warren Stutzman is a very useful reference. He has all the equations you could possibly desire....and a few more.
You may want to consider measuring with a rotating linear source. CP gain references can also be used. You might also want to illuminate your antenna with a suitably polarized (circular) source. I have made helicies in the past for this application (as a source). They are relatively easy to fabricate and match.
It is convenient that you have both phase and amplitude available, otherwise it would be difficult to determine CP direction and detect the difference between slant 45 deg and circular polarizations.
You don't say where you are in the frequency range or the type of antenna you measuring. My comments assume microwave band antennas and far field measurements.
Attached article explains the COMPUTATION AND MEASUREMENTOF THE POLARIZATION ELLIPSE