Zero-Knowledge Adaptive Beamforming using Analog Signal Processor for Satellite Tracking Applications with an Experimental Comparison to a Digital Implementation

A novel analog circuit for adaptive beamforming in an ultra low profile stair-planar phased array antenna system for mobile broadcast satellite reception in Ku-band is presented and its performance experimentally compared with digital beamforming control. The novelty of this method is that it performs gradient descent using an entirely analog feedback path. The beamforming algorithm compensates for the fabrication inaccuracies of the microwave components and variations in their characteristics due to ambient changes. Neither a priori knowledge of the satellite's direction nor the phase-voltage characteristic of the phase shifters are required in this implementation which results in eliminating an expensive laborious calibration procedure. The circuit performs continuous-time gradient descent using simultaneous perturbation gradient estimation. Field tests were performed in a realistic scenario using a satellite signal. The optimizer can converge in less than 50 ms and easily tracks antenna motions of greater than 60°/s. There are significant savings in terms of system cost, power consumption, and system integration complexity by switching to an integrated analog implementation.