Low-Profile Vertical Polarized Slotted Antenna for On-Road RFID-Enabled Intelligent Parking

A low-profile vertical polarized antenna is presented for radio frequency identification (RFID)-enabled intelligent parking system applications. In order to reduce the crosstalk between antennas and false detection of vehicles in the parking zone, a bidirectional antenna with low vertical obstacle is required by industry. To that end, a low-profile cavity-excited magnetic dipole-based antenna with vertical polarization is designed. Two vertical sides of the antenna are kept open for the easy access of the reader and powering components. In order to increase the polarization purity along the intended sides, a rectangular truncated ground plane is proved to be beneficial compared to a typical square shaped one. The overall structure of the on-road antenna over the ground plane is around 0.2 × 0.55 × 0.06 λ
₀
³
(λ
₀
is the free space wavelength of the center frequency). The design process and operating principle of the antenna are described in detail along with the effects of different parameters. The antenna is prototyped and measured. The antenna attains high reflection coefficient of -20 dB over 912-930 GHz covering the intended Australian ultrahigh-frequency (UHF) RFID band. The antenna demonstrates bidirectional radiation patterns having a maximum gain of 5 dBi over the required band with -20 dBi cross-polarization level. On-road measurements of the prototype show that the 3 dB beamwidth extends to ±90° elevation angles, which provides high read range while the tags embedded in the vehicle's license plate are in low elevation. The antenna has a rugged structure to sustain more than 10 years in regular road and traffic conditions. By meeting all the requirements, it has been proved to be an effective part of the on-road RFID-enabled intelligent parking system.