Linear Retro-Beam Scanning Array System

A unique beam scanning array, neither applying spherical-to-plane wave transformation like a reflect array nor utilizing corporate feed network like a Butler matrix, is proposed and investigated in this paper. The governing equations of a common retro-directive array are revisited and generalized to fulfill a linear array having retro-beam scanning without using heterodyne technique. In the proposed scheme, the progressive phase difference between the adjacent antenna elements is controlled not only by the interconnecting line in-between but also by an extra phase term introduced by a newly added phase shifter. According to the theoretical prediction, the main beam of the retransmitted wave can be steered to an arbitrary direction irrespective of the direction of arrival (DOA) of the incident wave. A linear four-element quasi-Yagi array, controlled by 4-bit phase shifters, is applied as a preliminary proof-of-concept. An automated retro-beam scanning system integrated with a DOA estimation network and a low-cost microcontroller was then experimentally demonstrated to validate its capability to steer and re-transmit a randomly incoming oblique wave within ±30° from the normal incidence to a preset targeted direction without any manual control. The theoretical background, formulation, experimental results, and potential application scenarios are carefully discussed.