Groundless Endfire Antennas Based on Spoof Surface Plasmon Polaritons

In this paper, a spoof surface plasmon polaritons (SSPPs) based groundless endfire antenna is proposed, which is composed of SSPPs guiding structure and a feed monopole. Through optimizing geometric parameters of the antenna configuration, electric field from the monopole can be coupled to SSPPs mode, which propagates on the SSPPs guiding structure and radiates at the structure end, leading to endfire radiation pattern. Because SSPPs mode is excited in near field zone, and SSPPs have properties of deep sub-wavelength and field confinement, the proposed antenna has advantages of low profile, miniaturized size and easy to conform. As an example, an X band endfire antenna is designed, fabricated and measured. The measured results are in accord with the simulate ones, and show that the proposed antenna works over $9.0 \sim 10.8$ GHz with realized gain varying from 3.27dB to 6.6dB. Radiation performances of the antenna conformed to a cylinder are also simulated. And the results show that the proposed antenna obtains high-efficiency radiation performances in conformal antenna design.