Compact Multibeam Dual-Frequency (24 and 77 GHz) Imaging Antenna for Automotive Radars

2 versions of a compact multi-beam dual-frequency antenna for 24 and 77 GHz have been developed for automotive applications. The antenna consists of a spherical Teflon lens with a frequency selective surface (FSS), which is fed by two sets of endfire tapered slot antennas (TSAs). The FSS is built on a 127 ¿m-thick Duroid¿ substrate and is placed between two Teflon hemispheres, and is reflective at 24 GHz and transparent at 77 GHz in the first design, and is transparent at 24 GHz and reflective at 77 GHz in the second design. The TSAs for the 24 GHz and 77 GHz systems are built on a single piece of 254 ¿m-thick Duroid¿ substrate. The measured patterns result in E and H-plane patterns with a -3-dB beamwidth of 19° at 24 GHz and 5.5° at 77 GHz. The sidelobe level is better than ¿17 to ¿20 dB when the FSS is transparent and is better than ¿14 dB when the FSS is reflective. The calculated efficiency of this antenna system is around 50%. The current designs provide 33° coverage at 24 GHz (3 beams) and 55° coverage at 77 GHz (11 beams) in the first design, and 99° coverage at 24 GHz (7 beams) and 33° coverage at 77 GHz (7 beams) in the second design, but the angles can be changed to suit different coverage angles.