High-Precision Phase Shifting and Real-Time Calibration of Phased Arrays for Passive Millimeter-Wave Imaging Applications

Abstract

The design and calibration of high-precision analog phase shifters are crucial issues for phased arrays interferometric passive millimeter-wave imaging systems. In this paper, a high-precision analog phase shifter is presented for phased arrays interferometric passive millimeter-wave security sensing applications, which realizes analog phase shifting function by controlling high-precision DAC (digital to analog conversion) with FPGA. It is known that pre-measured phase delay of a phased array channel is a prerequisite for beam pointing control. However, since many active devices are included in phased array channel link, the phase delay would be affected by various factors such as device moving and ambient temperature. So, high-precision phase shifting of phased arrays could be achieved only by measuring and calibrating phases when all components of the system are under normal working conditions. The algorithm proposed in this paper makes it possible to measure and calibrate phases when all sub-modules are integrated into the system, and each component is under normal working state, thus effectively avoiding the errors caused by environmental changes when the laboratory-measured results are put into practical use. Meanwhile, the algorithm is tested on Ka-band phased arrays interferometric passive millimeter-wave imaging system. It turns out that the phase accuracy of phased array channel can reach 5 • ± 1.5 • , and it only takes 2 minutes to complete the phase calibration of 256 arrays.