Dual-polarised end-fire antenna based on the high-order mode of spoof surface plasmon polaritons

A planar antenna with dual-linearly polarised end-fire radiation is proposed. A tapered double-sided symmetrical spoof surface plasmon polariton (SSPP) transmission line (TL) with tilted unit cells is proposed. The SSPP TL can operate in two types of first high-order modes: the first high-order even mode and the first high-order odd mode. A two-port feeding structure is designed to feed the SSPP TL. When the signal is fed from port 1, the energy travels through the substrate integrated waveguide and eventually excites the even mode on the SSPP TL, leading to vertically polarised radiation. Conversely, when the signal is input from port 2, the energy travels through the stripline-to-slotline transition and eventually excites the odd mode on the SSPP TL, generating horizontally polarised radiation. According to the measured results, a 54.6% overlapping bandwidth is obtained. The horizontal and the vertical polarisations achieve a maximum gain of 14.7 and 12.2 dBi, respectively.