A retrodirective array for mobile communication systems

Abstract

Retrodirective array is a kind of the phased array which has an interesting characteristic-a unique function of automatically responding by transmitting a signal back to an interrogator’s direction without any prior knowledge of the incoming signal’s location. The whole process does not include complex circuits like phase shifters, or techniques like comparing the difference of arrival time by using digital signal processing (DSP) circuits. It just relies on analogue operations. Hence, recently, a number of researches have been studied simply because of its simpler design, fast response (no time delay with some DSP components), and cost effective. In this project, 2-Dimensional retrodirective array is focused and it can be divided into three main parts. The first part is a new 2-D Van Atta antenna array using 8 dual-feed star-shaped elements operating at 5.8GHz, which aims at receiving and transmitting the signals. The scan range of this array is ±60° along the normal of the antenna array. Secondly, a phase-conjugator is used to make the reflecting signals (from array) being phase-conjugated with the incoming signal. This phase-conjugator (mixer) can achieve for about 45dB isolation between RF signal (5.8GHz) and IF signal (5.81GHz) and its conversion loss is about 6-7dB. The last part is a Wilkinson power divider for inputting one 11.6GHz (LO signal) and result in 8 of the 11.6GHz output signals in equal magnitudes altogether. At the same time, these signals are injecting the phase-conjugator respectively and then radiated by the antenna array. The whole module of this 2-D retrodirective array demonstrates a wonderful performance on 2-dimensional retrodirectivity and its scan range is ±45°, valid for any polarization e.g. linearly polarized (LP) and circularly polarized (CP).