An ultra-wideband 3 × 3 Butler matrix with unique Vivaldi array structure for high-range resolution radars

Steerable antenna beam capability is an outstanding expectation for the development of automatic tracking systems and target detection. A switched beam array antenna, which can generate multiple fixed beams with enhanced sensitivity, emerges as a solution for beamforming tracking. On the other hand, it is known that the target can be detected with high-range resolution thanks to ultra-wideband (UWB) systems. In this work, a compact switched beam Vivaldi array antenna based on a Butler matrix for a UWB application capable of target detection with accurate target tracking is presented to meet the high gain and low side lobe level requirements. Based on a three-element antenna array, two methods have been applied to obtain small grating lobes and it has been shown that significant improvements can be achieved. Designed with a 3 × 3 UWB Butler matrix, the UWB array antenna can direct its beams in three directions in a direction range from −42 to 42°. The measured result showed that the group delay was less than about 4.5 ns with variation of less than ±0.7 ns over the entire operating frequency band.