Quadruple-mode Resonant Broadband High-gain Backfire Vehicular Antennas

A novel design approach to a multi-mode wideband high-gain backfire vehicular antenna is proposed. The proposed antenna is an air dielectric microstrip path antenna, it is composed of a symmetrically fed sector principal radiator, an annular sector reflector and two annular sector directors all installed above a metallic planar ground. Firstly, through mode synthesis calculation, the sector principal radiator is designed to operate in the TM_{3π/α, 1} mode, thereby determining its central angle and radius. Then, initial parameters of the reflector and director are determined by using a multi-point equivalent source model for backfire characteristics enhancement. Finally, the feasibility of the design scheme is verified through physical experiments. The measured results show that the antenna exhibits a wideband, four-mode resonant characteristic from 4 GHz to 6.41 GHz (|S₁₁| < -10 dB), the impedance bandwidth is 46.3%. It is verified that maximum backfire gain has been enhanced to 8.9 dBi in 5.9 GHz V2X-band.