A Mixed Circular/Linear Dual-Polarized Phased Array Concept for Automotive Radar—Planar Antenna Designs and System Evaluation at 78 GHz

A planar antenna array front end for automotive applications in the 78 GHz band is discussed and evaluated. Separate antenna arrays for transmit and receive are realized on RF substrate with the objective to provide a very cost-effective and compact design. The basic array column consists of 10 dual-polarized square patch elements and launches a fan beam that illuminates a wide sector in azimuth but a narrow sector in elevation. The orthogonal linear polarizations are combined via a microstrip quadrature power splitting network in order to excite a single circularly polarized wave on transmit. On receive, the array column is arranged multiple times next to each other to allow for digital beamforming in azimuthal direction. A prototype consisting of three receiving columns has been fabricated and measured. Grating lobes are reduced to an overall sidelobe level of less than -10 dB by a time-division multiplex scheme that switches through several transmit arrays in different locations. Radar system simulations based on the measured antenna patterns demonstrate a very good discrimination of elementary polarimetric scattering objects.