Spherical Near-Field Measurements in a CATR at Low Frequencies

Author: Marion Baggett
Publication: AMTA 2024
Copyright Owner: NSI-MI Technologies

The size and optics of a Compact Antenna Test Range (CATR) determine its quiet zone and the lowest frequency at which it will meet nominal quiet zone specifications. If a reflector is not large enough to present a sufficient multi-wavelength surface at a given frequency, a plane wave is not generated. Operating compact ranges at lower and lower frequencies is a continuing desire in the measurement community. The normal solution for both instances is to increase the reflector size. This leads to larger test chambers, hence increasing cost. Collecting spherical nearfield (SNF) data in a CATR within its normal operating frequency band is well known. However, this leads to collecting more data than required to obtain principal plane cuts in the CATR. This paper presents a study and empirical data on using low-frequency range antennas that operate down to one half the nominal CATR low frequency using SNF techniques to measure test articles at these frequencies with relative accuracy. The paper includes simulations of the quiet zone performance at low frequencies.

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