Retrodirective array using direct down-conversion and fixed point DSP for duplex digital communications

Abstract

Adaptive and multi-antenna systems will be an integrated part of the future wireless world. In this paper, a novel low cost implementation of a self phased retrodirective array using direct RF conversion and coherent digital modulation in the uplink and downlink is presented. The transceiver is designed to receive and demodulate digital signals of arbitrary modulation type up to 100 ksymbols/s while at the same time directs its main beam back in the direction of the source using any vector digital modulation scheme at speeds up to 20 ksymbols/s. A direct conversion receiver is employed here in combination with a low-power fixed point digital signal processor, eliminating the need for an IF modulator and carrier recovery unit, this makes the design particularly attractive for a commercial application. Measured results of the uplink antenna pattern are presented and show the system has good retro directivity with beam pointing error less than three degrees in the angular range of -45 degrees to +45 degrees.