Low-Profile Antenna With Elevated Toroid-Shaped Radiation for On-Road Reader of RFID-Enabled Vehicle Registration Plate

A low-profile antenna installed on the road surface for RFID-enabled vehicle communication is presented. The antenna in this application operates as on-road sensor for vehicles identification. To that end, the antenna is required to have an elevated toroid-shaped radiation, so that the reader can easily interrogate an RFID-enabled vehicle license. The antenna is designed using a capacitive-loaded inverted-F radiator, which has an omnidirectional radiation in the azimuth plane. To adjust the radiation pattern to the required elevation above the road surface, and isolate the radiation from the effects of variable road conditions, a corrugated ground plane with perturbed surface impedance is used underneath the radiator. The antenna's configuration is verified by full-wave finite difference time domain simulations with various road surface conditions. A prototype antenna is then developed and tested in realistic field scenarios as on-road sensor for vehicles identification. The results show that the antenna possess more than 15 dB return loss, more than 1.5 dBi gain, vertical polarization, and desirable radiation pattern from 880 to 960 MHz, which is the standard band licensed for RFID-enabled plates. The antenna also successfully communicates with an RFID-enabled vehicle registration plate.