The Design of Miniaturized Planar Endfire Antenna With Enhanced Front-to-Back Ratio

A planar endfire antenna with enhanced front-to-back ratio (FTBR) and miniaturized size in its endfire direction is investigated in this communication. The antenna mainly consists of two closely placed dipoles with a small spacing of 0.04 lambda(0). By using a novel topology, the desired phase difference between the two dipoles is obtained to improve the peak FTBR up to 30 dB and the peak gain to 6.5 dBi. Furthermore, a parasitic strip and a series of grooves are introduced to the antenna to adjust the phase difference and the current distributions of the two dipoles, effectively expanding the 20 dB FTBR bandwidth from 2.3% to 13.3%. Consequently, the antenna with an overall size of 0.161 lambda(0) x 0.43 lambda(0) x 0.009 lambda(0) obtains an overlapping bandwidth (vertical bar S-11 vertical bar < -10 dB and FTBR >20 dB) of 8.3%, an average gain of 5.1 dBi, and a high efficiency of about 90%.