A Mode-Superposed Microstrip Patch Antenna and Its Yagi Array With High Front-to-Back Ratio

摘要

A new microstrip patch antenna with a linear superposition of its even and odd modes is proposed for a high front-to-back (F/B) ratio. With the mode superposition, the patch antenna has its main beam in the forward quadrant space and an inherent high F/B ratio. The antenna exhibits a vertical polarization in the ground plane. With a low proule, the patch antenna generates a wide impedance bandwidth though a relatively narrow radiation bandwidth (F/B > 15 dB). In order to have a wider radiation bandwidth with a high F/B ratio, a vertically polarized Yagi array antenna is constructed based on the patch antenna, with an electromagnetic band gap (EBG) structure as a reflector and a quarter-wavelength patch antenna as a director. (The employment of the EBG structure is helpful for the enhancement of the F/B ratio, but it increases the array size on the other hand.) Measured results show that the constructed Yagi array antenna with a low proule of 0.025λ₀ achieves an impedance bandwidth of 11.5% (4.83-5.42 GHz) for |S₁₁| <; -10 dB. Moreover, it has a wide radiation bandwidth of 10.1% (4.90- 5.42 GHz), in which the F/B ratio is higher than 15 dB and the gain is from 8.5 to 9.5 dBi.