Ultra-Wideband Planar End-Fire Antenna Based on High-Order Modes of Spoof Surface Plasmon Polaritons

In this article, an ultrawideband planar end-fire antenna based on high-order modes of spoof surface plasmon polaritons (SSPPs) is proposed. First, a quad-band end-fire antenna is designed by using the first four high-order SSPP modes. An SSPP transmission line with gradually decreasing groove depth is used to radiate the high-order modes. Moreover, to improve the gain and sidelobe level at high frequencies, the SSPP units in the quad-band antenna are tilted. Then, an SSPP structure consisting of a periodic array of metal strips is proposed. By adding two arrays of tilted I-shaped strip resonators to the quad-band antenna, the first two bandgaps are eliminated. The proposed antenna achieves a fractional bandwidth of 140.8% from 6.9 to 39.7 GHz. Minimum and maximum measured gains of 6.4 and 15.2 dBi are achieved at 6.9 and 38 GHz, respectively. The proposed antenna has a great potential for applications in imaging and wireless communication.