Substrate Integrated Antennas for Millimeter Wave Automotive Radars

Millimeter wave automotive radars are more and more popularly used to improve drivers' comfort and safety. High‐performance and cost‐effective radar sensor is always desired for the automotive industry. The antenna system is one of the key differentiating factors of an automotive radar sensor that defines the field of view and achievable angular object separation. The substrate integrated antenna is an excellent candidate for automotive radar sensors owing to the merits of planar configuration, light weight, low cost for material and fabrication, and easy integration with RF front‐end. This chapter focuses on the printed circuit board (PCB)–based high‐gain substrate integrated mmW antennas for car radar sensors. First, the general aspects of automotive radar are addressed including the classification, the frequency band regulation, system requirements, and antenna design considerations. Second, the state‐of‐the‐art antenna designs for 24 GHz and 77 GHz automotive radars are reviewed. After that, two types of antenna arrays are introduced. A compact co‐planar waveguide (CPW) center‐fed substrate integrated waveguide (SIW) slot antenna array is elaborated to achieve narrow H‐plane beamwidth and low sidelobe levels for 24 GHz automotive radars. A transmit‐array on dual‐layer PCB is introduced for automotive 77 GHz radar applications. With four SIW slot antennas as the primary feeds, the transmit‐array is able to generate four switched beams. The coplanar structure significantly simplifies the transmit‐array design and eases the fabrication, in particular, at millimeter‐wave frequencies.