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Author for correspondence: Grigory Kuznetsov, E-mail: [email protected]
Introduction
Development, calibration, and testing of active phased antenna arrays require solving a large number of problems, including the problem of diagnosis of the array under test (AUT). Many factors determine the selection of the diagnosis method: structure and operating mode of AUT during the testing, diagnosis duration (including duration of measurement and computation), and cost of its implementation. The results of the diagnosis problem solution allow estimating the technical condition of the active array and determining how its characteristics differ from the required ones. These differences may be caused by failures of single or groups of transmit-and-receive modules (TRMs), including failures of phase shifters, switches, and amplifiers [1,2].
Especially strict performance requirements are imposed on space-borne systems, particularly synthetic aperture radars [2,3]. Ground testing of active arrays includes measuring not only radiation characteristics (far-field pattern, sidelobe level, equivalent isotropic radiated power, cross-polarization level, mutual coupling between elements) but also impedance matching, power loss, and power consumption.
Many radiation characteristics of electrically large active arrays can only be measured in an anechoic chamber using near-field techniques, because the far-field zone distance may be prohibitively large. After the initial calibration of the phase shifters and attenuators of the array, a testing in normal operating mode, i.e. with all TRMs turned on, is required.
On this step, a testing of the antenna in a wide temperature range (tens and hundreds °C) should be performed [4,5], since the characteristics of TRMs significantly depend on temperature. The measurement duration of active arrays compared to passive antennas is limited by three factors. First, the service life of TRMs is limited. Second, the TRMs warm up during the operation, and change their characteristics. Third, the duration of the normal operating mode of the whole system is also limited.
Conventional methods of phased antenna array diagnosis include measurement of the full set of field data in the near- or far-field zone [6,7]. These methods, including methods based on the solution of integral equations using the method of moments, do not utilize a priori information about a reference, non-defect array. It leads to a large dimensionality of the problem, and the resulting computational problem is ill-posed [8]. For an array of N elements, the number...