Bandpass Filter Based on High-Order Mode of Spoof Surface Plasmon Polaritons

A bandpass filter is proposed in this paper by utilizing the high-order mode of spoof surface plasmon polaritons (SSPPs). The adopted SSPPs unit cell is a Yagi-like antenna structure, which can effectively reduce the asymptotic frequency of the SSPPs. In addition, the asymptotic frequency of the mode 1 and the intersection frequency with the light line in free space can be manipulated by adjusting the geometric parameters of the SSPPs unit cell. Compared with the fundamental mode with low-pass characteristics, the mode 1 has inherent band-pass response and does not require an additional gradient transition structure for excitation. In order to verify the feasibility of proposed high-order mode based bandpass filter, a topology is fabricated and measured by the vector network analyzer. The measured results show that the insertion loss is less than 1 dB from the frequency range of 6 GHz to 9. 9 GHz, and the in-band return loss is better than 10 dB, which is in agreement with the simulated ones.