Design and Experimental Validation of a Passive Van Atta Retroreflector Array in Gap Waveguide Technology

Abstract

Automotive radar operating in the 77 GHz frequency band is increasingly implemented in modern cars. A challenge these radars face is the detection of vulnerable road users, such as pedestrians, whose radar cross section (RCS) can be low and highly variable. Compact passive retroreflectors, such as Van Atta arrays, can increase their radar visibility, but when implemented with patch antennas or substrate integrated waveguides (SIWs), these arrays suffer significant dielectric losses at mmWave frequencies. Motivated by this limitation, this work uses Multilayer Waveguide (MLW) technology as the basis for a passive Van Atta array intended to enhance RCS over the 76–81 GHz frequency band. This is done by designing, modeling, manufacturing, and experimentally validating a prototype MLW Van Atta array. The prototype is designed for horizontal polarization and provides retrodirection in the azimuth plane. The Van Atta array consists of 12 slotted waveguide columns. Each column consists of six slots fed in series by a coaxial line in MLW. The columns are connected pairwise through transmission lines with equal electrical length. Several samples of the reflector are then manufactured and validated through an RCS measurement setup in an anechoic chamber. All measured samples demonstrate a functional angular range of more than 90◦ across the 76–81 GHz frequency band, with an operational bandwidth of approximately 5 GHz. Within this range, the designed retroreflector provides an RCS improvement of approximately 10 dB to 20 dB compared with a metal plate of the same physical size. These results show that compact planar Van Atta retroreflectors with a thickness below 1mm can be realized in MLW technology and provide wide-angle RCS enhancement. This makes the approach promising for increasing the radar visibility of vulnerable road users.