Electronically Scanned Left-Handed Leaky Wave Antenna for Millimeter-Wave Automotive Applications

Abstract

In the past few years, there has been significant interest in automotive radar for pre-crash safety and adaptive cruise control systems [1], [2] using a millimeter-wave band from 76 GHz to 77 GHz. In the systems, the beam is electronically scanned in the azimuth angle to detect vehicles and obstacles. Wide beam scanning and high gain are required as the radar antenna systems. Furthermore, compact size and low cost are important for automotive applications. The left-handed leaky wave antenna (LHLWA) is able to scan the beam widely because it supports both backward and forward waves [3]. However, the conventional frequency-dependent LWLHAs are not practical for the automotive radar antenna systems. In order to overcome this drawback, much effort has been made in developing the frequency-independent LWLHAs. An electronically and continuously scanned LWLHA using the varactor diodes was presented [4], but the diodes are too lossy to use in the millimeter-wave band. Moreover, it is difficult to fabricate high gain array antennas which have hundreds of unit cells and diodes. As other problems of the conventional LHLWAs, antenna gain is not enough for radar applications because the aperture amplitude distribution of the array antennas cannot be controlled well. We have proposed a novel structure of LHLWA, which can steer the radiation angle at a fixed frequency. The antenna includes a dielectric material, which locally changes its dielectric constant in response to an external stimulus. Liquid crystal has attractive properties such as a low electric command and weak losses in the millimeter-wave band. Moreover, slots are added to the LHLWA to control the aperture amplitude distribution of the array antennas.