24 GHz active retrodirective antenna array

A 24 GHz active Van Atta planar antenna array proposed for increasing the vehicle radar echo in a vehicle collision avoidance system is designed and demonstrated. The antenna array contains two parallel linear sub-arrays. Each sub-array is composed of four receiving microstrip antennas, four transmitting microstrip antennas and four transistor amplifiers. At the angles of -40°<θ<40°, except those very close to the specular direction (θ=0°), the measured backscattering field levels of the fabricated array have variations <3 dB and are at least 10 dB higher than those of a metal plate of the same size