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 λ
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 λ
₀
× 0.43λ
₀
× 0.009λ
₀
obtains an overlapping bandwidth (|S
₁₁
| <; -10 dB and FTBR > 20 dB) of 8.3%, an average gain of 5.1 dBi, and a high efficiency of about 90%.