High-Gain Wideband Filtering Quasi-Yagi Antenna Based on High-Order Mode of SSPPs

A high-gain wideband filtering antenna based on the high-order mode of spoof surface plasmon polaritons (SSPPs) is proposed. Excellent filtering characteristics with six radiation nulls (RNs) are obtained from the first high-order mode (mode 1) of SSPP feedline. A novel ground-free single-unit transition structure (GFSTS) is introduced to facilitate smooth momentum transition and impedance matching between the SSPP feedline and driven dipole. The inherent bandpass response of the high-order mode of SSPPs enables the proposed filtering antenna to operate without additional filtering structures, thus avoiding insertion loss and achieving a simplified design. The low-loss transmission characteristic of the SSPP feedline, along with the elimination of insertion loss from external filtering components, enhances the radiation efficiency of the quasi-Yagi antenna. To validate the feasibility of the proposed antenna, a prototype is fabricated and measured. Good endfire characteristics are obtained with a bandwidth of 3.76–6.3 GHz (50.5%), a peak gain of 9.98 dBi, and the out-of-band suppression larger than 18.8 dB. The measured results are in good agreement with the simulation.