Millimeter-Wave ATS Antenna With Wideband-Enhanced Endfire Gain Based on Coplanar Plasmonic Structures

Coplanar plasmonic structures are proposed to converge the beam of electromagnetic (EM) wave and to enhance the gain of an antenna. While propagating along the plasmonic structures, EM wave shows a larger propagation constant than that in free space due to the slow wave feature of spoof surface plasmon polaritons (SPPs) SPPs; i.e., it sees a higher equivalent refractive index. Therefore, a dielectric substrate sandwiched by plasmonic structures can be equivalently taken as a refractive index graded lens. To validate this concept, a millimeter-wave antipodal tapered slot (ATS) antenna loaded with the plasmonic structures is designed. The antenna shows merits of beam convergence both in the E-plane and in the H-plane, although the plasmonic structures are coplanar with the E-plane, and also a wide frequency band of gain enhancement due to the nonresonant characteristic of the SPPs. Compared with the reference ATS antenna with dielectric loading, the proposed one shows an additional gain enhancement of 2 dBi in the band of interest (22-27.5 GHz) and the peak gain of 15.5 dBi. The measured and simulated results agree well with each other, which effectively validates the convergence effect of the plasmonic structures in the antenna.