The Impact of Rotating Linearly-Polarized Feeds on Circularly-Polarized Gain Uncertainty

Authors: Adam Mehrabani, Rob Mercer, and Jeff Fordham
Publication: AMTA 2023
Copyright Owner: NSI-MI Technologies

This paper addresses the circularly-polarized (CP) gain uncertainty when using linearly-polarized feeds to obtain circular polarization in Compact Antenna Test Ranges. In particular, our emphasis is placed on quantifying the inaccuracy caused by deviations in amplitude and in phase of the two orthogonal linear measurements. This is of paramount importance especially for highly directive CP antennas operating at high frequencies in that the CP gain will be adversely impacted even by a small deviation from an ideal 90- degree rotation, as well as by a situation when the rotation may cause a slight boresight misalignment. To characterize the gain uncertainty, we look at ratio differences between the peak amplitude of the linear measurements, as well as cases when the phase shift of the two orthogonal linear measurements is no longer 90 degrees. The former is done through mechanical and electrical boresighting technique in the initial setting. The latter, which is the focus of this paper, is carried out through several case studies in practice mimicking some non-ideal 90- degree rotation settings.

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