A Wideband, High Gain and Low Sidelobe Array Antenna for Modern ETC Systems

Abstract

Modern electronic toll collection (ETC) systems are currently moving towards a system design that is capable of fast and optimal payment handling for a single lane. Thus, the antenna of a roadside reader unit (RSU) needs to provide sufficient coverage over the vehicle lane during a payment cycle. In this paper, a left-hand circularly polarized (LHCP) 2×4 array antenna is proposed for European standard RSU readers at 5.8 GHz. The proposed array antenna consists of patch element antennas with parasitic elements to enhance gain and bandwidth. Sequential phase rotation feeding networks are applied to make the antenna low-profile. By using the optimized nut-shaped metasurface, the antenna can achieve higher gain due to concentrated radiation power in the boresight direction. The antenna has a wide impedance bandwidth of 2.34 GHz (37.73%), axis ratio bandwidth of 2.07 GHz (32.9%), high gain of 17 dBi, and sidelobe level (SLL) lower than -15 dB at 5.8 GHz. Especially, half-power beamwidths are 34∘ and 17∘ in horizontal and vertical planes, respectively, which covers sufficient space for a single lane while avoiding interference with other lanes. The performance of the proposed antenna is verified by measured results. It showed that the proposed antenna is a promising candidate for ETC applications.