A high gain wideband array antenna based on metasurface for ETC application

Abstract

Free flow electronic toll collection (FFETC) has played an important role in building convenient and safe transportation systems in many countries. The most challenging problem when researching and developing this system is shortening the payment cycle so that vehicles passing through the stations do not need to stop or keep going at a speed greater than 60 Km/h. Designing roadside unit (RSU) reader antennas with high gain and suitable radiation pattern is the most feasible and economical solution. This paper proposes a left-handed circularly polarized (LHCP) 2×4 array antenna using sequential phase rotation power dividers at 5.8 GHz band. The element antenna is a square patch antenna with a slit in the middle for better impedance matching, six trapezoidal parasitic patches added to either side of the main patch to create resonance at high frequencies, and a metasurface placed on top of the main patch. The proposed metasurface is a 4×4 array of dual circular unit cells to improve gain and extend axial ratio (AR) bandwidth. The proposed antenna array has a high gain of 17 dBi, -3 dB vertical and horizontal beamwidths of 33.20 and 17.10, which cover over one lane, are expected for any ETC system to avoid interference with other lanes. Impedance bandwidth and AR bandwidth are 2.19 GHz (37.75%) and 2.06 GHz (35.52%), respectively. The overall dimensions of the proposed array antenna are approximately 152×76×6.4 mm3. With the above merits, this antenna is a suitable candidate for the RSU reader antenna in the FFETC