Axial Ratio Measurements

[Henry797]

I know the definition of Axial ratio of an antenna, which is the ratio of the transverse components of E-field of a particular antenna (circularly polarised antenna). I also know how to get the axial ratio (dB Vs frequency graph) from CST. Now if I measure the farfield patterns of my fabricated antenna in an EMC Chamber, how do I calculate the axial ratio from (dB Vs Scanning angle) data I get from measurements?
Can anybody seecialised on this topic help me?
Many Thanks in advance

 

[Darktrax]

Huge number of reads but no replies?

I don't have much experience at this either, but I have tried pointing a circular polarized antenna at a satellite signal of known circular polarization, and checking the signal on the "wrong" polarization connector on the polarizer. This was in no way a true measurement because of the many circumstances on the way that contribute to crosspolar signal leak, added to which, there is the characteristic of the polarizer.

Since your antenna is small enough (or your anechoic test facility is large enough) to be able to probe the farfield sans unwanted reflections, you can use an test probe antenna of exclusive linear polarization (eg. pyramidial) and point it straight at the test antenna. Rotating the test antenna axially will provide the series of measurements. Axial ratio is of course the dB ratio between the maximum and minimum seen, remembering that the dB ratio of voltages is 20*log10(ratio).

I get it that you may want to aim at your structure from various angles.

I would not pretend that I can much directly help you here, but getting some from search engines is easy.
Here at least is one that may be at least a start.

Axial Ratio (Microwave Journal) LINK --> https://www.microwavejournal.com/ar...ments-of-single-circularly-polarized-antennas

 

[viper_iv]

Which value exactly did you measure in the EMC Chamber? e.g. E field magnitude and phase in the horizontal or vertical plane.

 

[Henry797]

The farfield radiation pattern, both magnitude and phase (S21) where the magnitude of power received was measured against scanning angle

 

[viper_iv]

Check these Matlab scripts, they have a function to calculate directly the axial ratio (if I remember correctly).
http://labrf.av.it.pt/Data/Manuais ...as/Measurements Kits Antennas/Scripts MatLab/