Validation and Testing of Initial and In-Situ Mutual Coupling-Based Calibration of a Dual-Polarized Active Phased Array Antenna

Abstract

This paper presents experimental results of an initial and in-situ mutual coupling calibration techniques of an active phased array antenna. The antenna is a dual-polarized 64-element C-band subarray panel equipped with an RF beamformer that enables mutual coupling measurements. Both techniques were implemented, tested and validated using a custom anechoic chamber and a radar backend. The implementation of a radar backend enables the in-situ validation of both methods. A conventional near-field calibration procedure, also known as park and probe, was used as a reference, in order to validate the proposed method. To quantify the calibration effectiveness of the mutual coupling-based techniques, the results are translated into phase and amplitude errors. It is found that the amplitude estimation of the tested initial technique is affected by edge effects, resulting in errors larger than 1 dB, whereas the phase estimation is less sensitive, yielding an overall root mean square error (RMSE) of 2.5 •. In contrast, the proposed in-situ technique is not affected by edge effects, and its estimation RMSE is less than 0.12 dB in amplitude and less than 0.75 • in phase. Mutual coupling-based calibration techniques are demonstrated to be very versatile, as they provide calibration methods for environments outside an anechoic chamber, and they also enable immediate feedback on the health of the system. INDEX TERMS Active phased array, calibration, component failure, mutual coupling, park and probe.

Impact Analysis and Calibration Methods of Excitation Errors for Phased Array Antennas

“…It relies on the assumption that coupling between an antenna element and its neighbors are the same for all elements in the array. Nonetheless, it was revealed by using a prototype system, it does not hold for small arrays due to unwanted edge effects [70][71]. A before/after approach is introduced to avoid errors introduced by edge effects, the ratio between the after and before status will quantify the changes suffered by the elements.…”

“…These calibration methods vary from different systems and applications, either suitable for factory test or for in-field test [41]. Some methods such as the near-field scanning probe method and the peripheral fixed probe method require additional equipments [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60], while the mutual coupling method takes advantage of the inherent property of the phased array without the need for extra hardware [61][62][63][64][65][66][67][68][69][70][71]. For Si-based integrated phased array antenna, it's very common to design a dedicated coupling network that using transmission lines connected to each antenna element for periodic in-field calibration [72][73][74][75][76][77][78][79][80][81][82][83][84][85][86]…”

“…FIGURE 7. Coupling schemes for rectangular phased array calibration by performing the mutual coupling method[41,70].…”

Closed‐loop controlled microwave beamformer

“…On the other hand, the peripheral fixed probe method employs one or various fixed probes at the periphery of the array to create a reference signal for the beamformer calibration 32–35 . The mutual coupling method, in turn, uses the mutual coupling between the array radiators to perform the calibration 28–31 . The last calibration technique, the built‐in network method, on which this article is based, applies the reference signal to the beamformer through couplers connected to the terminals of the antennas 38,40,42–44 …”

“…In the literature, there are found four calibration methods to deal with this problem 24,25 . They are classified as near‐field scanning probe, 26,27 mutual coupling method, 28–31 peripheral fixed probe, 32–35 and built‐in network method 36–41 …”