Spoof surface plasmon polaritons based notch filter for ultra-wideband microwave waveguide is proposed. Owing to subwavelength confinement, such a filter has advantage in the structure size without sacrificing the performance. The spoof SPP based notch is introduced to suppress the WLAN and satellite communication interference simultaneously. Both the cutoff frequency and the notch frequency are sensitive to the structure parameters, and the cutoff frequency can reach 20 GHz. An adiabatic transition relying on gradient hole-size and flaring ground is designed to effectively couple energy into spoof SPP waveguide. The result shows its cutoff frequency of 17.4 GHz with the insertion loss better than 3dB during the whole pass-band, while having more than 20 dB rejections at 5.36GHz and 9.32GHz with 10dB fractional bandwidth 1.07% and 0.74% respectively to avoid the existing WLAN and satellite communication signals. Due to planar structures proposed here, it is easy to integrate in the microwave integrated systems, which can play an important role in the microwave communication circuit and system.

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Graphene has many novel properties such as the ability of guiding plasmonic wave at terahertz (THz) frequencies, chemical potential shift as the carrier density changed. Since carrier density of graphene can be modified by bias voltage, the coupling coefficients or propagation loss of graphene plasmon can be modulated easily. A compact wideband terahertz modulator is proposed to modulate and guide plasmonic waves. The SPP propagation and modulation depth in the graphene biased structure are numerically investigated. The proposed terahertz plasmonic modulator has a wide working band about 1 THz and its modulation depth reaches about 76% at the frequency of 8THz, which have potential application in terahertz communication.

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