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Ryan Cutshall, Justin Dobbins, Jacob Freking, Brandon Hertneky, October 2022

A new far-field valid angle equation for rectilinear planar near-field measurements is presented. The new valid angle equation was derived by viewing the planar near-field to far-field transformation process as generating a set of pseudo plane waves by a synthetic phased array and subjecting the antenna-under-test to the radiation from this synthetic array. The synthetic phased array does not physically exist; rather, the array is formed during the post-processing of the planar near-field measurements. As part of this discussion, we present results from a numerical model, illustrating the total electric field present in the test zone due to the finite extent of the synthetic phased array.
The new far-field valid angle equation accounts for the diffraction effects of the finite-sized synthetic array, and uses the industry accepted test-zone magnitude ripple of +/- 0.5 dB to limit the valid far-field angle for a fixed scan plane size. The resultant valid far-field angle computed with the new equation is compared against previously established and popularly accepted valid angle equations, such as the equations previously presented by Yaghjian, Maisto, and Joy [1, 2, 3].
Brief discussionsare offered on the measurement of low directivity antennas with a planar near-field measurement system, and on amplitude tapering of the near-field measurements to improve the quality of the pseudo plane wave.
REFERENCES:
[1] A. D. Yaghjian, "Upper-bound errors in far-field antenna parameters determined from planar near-field measurements, part 1: analysis," National Bureau of Standards (NBS), Boulder, Colorado, USA, vol. Technical Note 667, no. October 1975.
[2] M. Maisto, R. Solimene and R. Pierri, "Valid angle criterion and radiation pattern estimation via singular value decomposition for planar scanning," IET Microwaves, Antennas & Propagation, vol. 13, no. 13, pp. 2342-2348, 2019.
[3] E. B. Joy, C. A. Rose, A. H. Tonning, and EE6254 Students, “Test-zone Field Quality in Planar Near-field Measurements,” in Proceedings of the 17th Annual Meeting and Symposium of the Antenna Measurement Techniques Association, Williamsburg, 1995.