Millimeter wave array for UAV imaging MIMO radar

Abstract

High resolution imaging radars at millimeter-wave frequencies for obstacle avoidance for Unmanned Aerial Vehicles (UAV) utilize a large antenna aperture and sequential mechanical scanning of the aperture to form images with high fidelity. Planar arrays are an attractive alternative. They do not require mechanical scanning, and images are formed digitally using beamforming techniques [1]. To achieve image quality comparable to mechanically scanned radars, fully populated arrays require inordinate numbers of elements. These are costly, a challenge to design, and difficult to produce. Thinned or sparse arrays are a potential solution to this problem. MIMO (Multiple Input Multiple Output) techniques are an efficient method of thinning an array using spreading sequences to create an overlay of paired transmitter and receiver elements, without sacrificing image quality. The use of MIMO techniques to thin an array is a relatively recent development [2]. To be of practical use at millimeter-wave frequencies, MIMO techniques require the development of novel array geometries and architecture. This paper presents designs for the implementation of millimeter-wave planar arrays which have been thinned using MIMO techniques and considerers the limitations on the length of spreading sequences due to the increasingly pronounced effect of Doppler at higher frequencies. These considerations have led to the first instance of the use of the Moreno-Tirkel sequence Family B for high resolution imaging radar.