A method for measuring amplitude and phase of each radiating element of a phased array antenna

Abstract

In the phased array system, excitation amplitudes and phases based on the design are specified for each antenna element in order to synthesize desired beam scannings and radiation patterns. However, due to fluctuations of antenna and feed network characteristics, the amplitude and phase of each antenna element deviate from the desired values. To correct these deviations, the amplitude and phase of each antenna element must be accurately measured under specific operating conditions. In this paper, we employ variable phase shifters connected to the antenna elements and measure only the amplitude variation of the composite electric field of the entire array when the phase of each element is modified. The rotating element electric field vector method in which the measured amplitude variation is numerically processed for obtaining the amplitude and phase of the particular element is theoretically discussed and experimentally tested for its usefulness. The present method can be easily attained by simply adding software to the computer‐controlled phased array system.

Theoretical study on measurement accuracy of rotating element electric field vector (REV) method

“…A.1 when the excitation phase of element m is varied by 360°. Then, the excitation amplitude and excitation phase of the element electric field of element m is given by the following equation, under the conditions of assumption (E) [1,10]: Hence, by using these relationships, the following three equations can be obtained:…”

“…This is an appropriate assumption. Assumption (E) is valid for a general array antenna and is used for specifying the operational equation in the derivation of the element electric field amplitude and phase by the REV method [1].…”

“…Therefore, even if the excitation phase of the element is varied by 360° in accordance with the measurement principle of the REV method, the variation of the array combined power may not be a perfect cosine curve. Therefore, the amplitude and phase of the element electric field are measured by extracting the cosine curve components by means of the Fourier transform, or by least-squares approximation of the obtained variations of the array combined power [1,10]. The measured element electric field values obtained in this manner naturally contain measurement error, which leads to the phased array calibration error.…”

“…The rotating element electric field vector (REV) method is a method of measuring the radiating electric field (element field) of each element antenna (element) in a phased array [1]. This measurement method takes advantage of the fact that the combined power of the array antenna (array combined power) is cosinusoidal (cosine curve) when the excitation phase of the element to be measured is varied by 360° so that the relative amplitude and relative phase of the element electric field are measured.…”

“…Since the REV method has extremely attractive characteristics, it is widely used for calibration of phased arrays [1][2][3][4][5]. The method is also applied to the self-diagnostic systems of phased array antennas [6,7], to near field measurement carried out with only the amplitude [8], and beam pointing by measurement at several observation points [9].…”