Broadband Dual-, Triple-, and Quad-Resonance Endfire Antennas Based on Surface Waves

Three simple planar endfire antenna designs, in which surface-wave guides (SWGs) and a high-impedance surface (HIS) are used, are presented in this communication. These antennas support dual, triple, and quad surface-wave resonances, and exhibit wideband performance and high-gain potential. The HIS with a wide bandgap is used to prevent the propagation of the supported surface waves along a desired direction, and thus the endfire radiation tilted to the other direction is generated. The eigenvalue is adopted to explain that only TE
₀
-mode surface waves are excited, and the characteristic mode analysis is presented to illustrate resonances of the tree antennas and explain why there are more resonances when the truncated number of the SWG increases. These antennas are fabricated and measured, and measured results validate the wideband and stable-gain performance.