A Ka-Band Scalable Hybrid Phased Array Based on Four-Element ICs

Abstract

In this article, a scalable hybrid phased-array system is presented through synchronization, analog complex weighting, and digital beamforming of numerous fully integrated Ka-band four-receiver (RX)/four-transmitter (TX) phased-array transceiver integrated circuits (ICs). A 1.09-GHz clock synchronizes the local oscillator (LO) and a 50-MHz clock synchronizes analog-to-digital (A/D)/digital-to-analog (D/A) converters for all array elements. Phase shifting is first accomplished in the analog domain using optimal intermediate frequency (IF)/LO complex weighting and signal summing in the 4RX/4TX IC to reduce the number of signals by a factor of four, followed by A/D sampling and digital beamforming in field-programmable gate arrays (FPGAs) and central processing units (CPUs). Phase-shifting properties, programmable gain variations, and antenna patterns of each RTX channel are measured and tabulated to calculate the optimal channel weights. The long-term phase stability is enhanced through temperature control by monitoring all ICs' temperatures in real time and adaptively adjusting the duty cycle of the TX mode of each IC to limit instantaneous temperature variations to +/- 0.5 degrees C over each calibration session. This reduces random phase errors from 13.3 degrees to 4.8 degrees in the TX mode. After each Vivaldi antenna is located on a 2-D rectangular grid, an 8 x 4 subarray module with synchronized digital output is demonstrated. With the boresight pointing along the x-axis, the eight-element dimension pointing along the y-axis, and the four-element dimension pointing along the z-axis, this subarray steers radiation patterns with the E-field polarized to the y-axis between +/- 40 degrees in both azimuth and elevation with 13.4 degrees and 26.4 degrees measured 3-dB beamwidths, respectively.