Hello,
My AUT is a circularly polarized antenna. I want to measure its radiation pattern so I have kept it as the receiving antenna in my set-up. What difference shall I observe in the measurement of the radiation pattern in the following two cases?
1. The transmitting antenna is a linearly polarized antenna
2. The transmitting antenna is a circularly polarized antenna
Thank you, Yang.
But what about the radiation pattern? Will it be the same?
If your AUT is a CP antenna;
Case 1: If Tx is an LP, you should get more directive but high gain radiation pattern.
Case 2: If Tx is CP, you should get less directive (Omni) but low gain radiation pattern.
Note: LP Tx antennas work better for planar Rx.
If your antenna is perfectly circularly polarized in all directions then a linearly polarized antenna will measure 3 dB less gain in all directions but the correct pattern shape. If the circular polarization is not ideal then the linear polarization could measure a completely wrong polar diagram. One way round that is to continuously spin the linear antenna, which will show how circular the polarization is (or not), but not the sense of circular polarization, so it will not show which directions have the opposite hand of polarization to what you want.
The reliable results can be achieved if your AUT is a planar CP antenna and transmission is done with an LP antenna during measurement.
what is AUT ?? i m not getting this can you please explain it to me
thankx
Muhammad is mistaken - using a linearly polarized antenna to measure a circularly polarized antenna only gives the right answer (3 dB down) if the AUT is perfectly circularly polarized in all directions measured - and no antenna is perfectly circularly polarized in all directions. Using linear polarization will not tell you if you have RHC (right hand circular) or LHC, or if you have elliptical polarization (a mixture of circular and linear, or a mixture of RHC and LHC).
Spun linear is better but will not tell you whether it is LHC or RHC but it will give axial ratio (how circular it is, or the ratio of LHC and RHC).
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