Spoof Surface Plasmon Polariton Endfire Antenna Possessing Bidirectional and Unidirectional Radiation Pattern

A simple approach is proposed to design a new type of endfire antenna, which simultaneously possesses bidirectional and unidirectional radiation pattern in wideband. By the dispersion engineering, different frequency bands spoof surface plasmon polariton (SPP) modes are excited at the two ports of a proposed splitter structure, and the two ports of the splitter structure are directly connected with two radiator structures, which are utilized to decouple the different frequency bands spoof SPP to free space wave by dispersion mismatching, achieving bidirectional and unidirectional radiation pattern in different frequency bands. From 8.4 to 21.6 GHz, this designed spoof SPP antenna possesses bidirectional endfire radiation pattern, and from 21.6 to 45.0 GHz, this designed spoof SPP antenna possesses unidirectional endfire radiation pattern. This designed spoof SPP antenna has an average gain over 10.6 dB in the whole working bandwidth, and the relative bandwidth of this antenna is 137%. Both the simulation and measurement results verify that the stable bidirectional and unidirectional radiation pattern of this proposed endfire spoof SPP antenna in wide bandwidth are achieved.