In this paper, we present a novel broadband bandpass filter based on spoof surface plasmon polaritons (SSPPs) in the microwave frequency band. The proposed bandpass filter includes three parts: (1) coplanar waveguide (CPW); (2) matching transition; and (3) coupled structure that is an asymmetric coupled filter constructed by five grooved strips. The proposed bandpass filter realizes excellent low loss performance from 7 to 10 GHz, in which its insertion loss is around 1.5 dB in the same frequency band. Meanwhile, this filter has a good band stop characteristic from 3 to 7 GHz. A simple but accurate transmission line model was proposed to evaluate the proposed broadband SSPPs filter. The measured data, simulated results and the results obtained from the transmission line model have shown a very good agreement. The proposed planar broadband filter plays an important role for filtering surface plasmon polaritons (SPPs) waves in plasmonic circuits and systems.

In this letter, a coplanar waveguide (CPW) filter based on spoof surface plasmon polaritons (SSPPs) in the microwave frequency band is proposed, which can achieve multi-band transmission by using periodic holes etched on the middle line of a CPW. Compared to the conventional SSPP designs, the proposed SSPP-based waveguide filter removes the gradual structure for the mode conversion. Simultaneously, the transmission efficiency of high-order modes is obviously improved by employing periodic holes etched on both the side grounds of the CPW. The physical mechanism of the proposed SSPP-based waveguide filter is explained with the aid of the dispersion curves and electric field distributions. Experimental results validate the proposed concept, and the measured results are in good agreement with the simulated ones, which indicates that the proposed SSPP-based waveguide filter can find potential applications in plasmonic integrated circuits at microwave frequencies.

A wideband dual-polarized omnidirectional antenna is proposed for mobile communication base station and 2.4-GHz wireless local area network (WLAN) applications. An integrated design is achieved by combining an inverted-cone monopole for vertical polarization (VP) and a modified cross bow-tie dipole for horizontal polarization (HP). The proposed antenna has a compact size because the HP element acts as the HP radiating element and the ground plane for the VP element simultaneously. The proposed VP and HP antennas are excited by a 50-Ω SMA connector and a broadband feeding network, respectively. The overall volume of the proposed antenna is only 0.35 λ0×0.35 λ0×0.25 λ0 (with λ0 being the wavelength of the lowest frequency). Simulated results show that the dual-polarized omnidirectional antenna achieves a bandwidth (for | S 11|< -10 dB) of about 41.5% (1.64 to 2.5 GHz) with an isolation of at least 25 dB and the gain variations at the center frequency in the horizontal plane are 0.7 dB for VP and 2.3 dB for HP. The good agreements between the simulated and measured results validate the proposed design.

An efficient method to split spoof surface plasmon polaritons (SSPPs) to different directions is proposed by designing a low-loss SSPP waveguide in an ultrawide frequency band. For this purpose, a coplanar-waveguide-based SSPP structure with double-row hole arrays etched on its middle line is first studied, which can be easily used to split the SSPP waves. Based on this method, a Y-shaped $-3\mathrm{dB}$ SSPP power divider and its application on a Mach–Zehnder interferometer are presented. The experiment demonstrates that the proposed method splits the SSPP waves to different directions effectively in ultrawide frequencies (2.5–39.7 GHz) with good isolations, indicating that the proposed SSPP power divider can have good application on a Mach–Zehnder interferometer and plasmonic integrated circuits.

A wide-angle frequency beam scanning antenna based on spoof surface plasmon polaritons (SSPPs) is proposed for planar integrated communication circuits. The SSPP-based antenna is constructed by hole arrays etched on the standard 50 Ω coplanar waveguide, which can achieve ultrawide bandwidth and wide-angle beam scanning from backward direction to forward direction as the frequency changes. The radiation mechanisms of the SSPP-based antenna are based on the higher-order modes of the structure, which have been analyzed by the dispersion curves and electric field distributions. The overall width of the proposed SSPP-based antenna is only 0.95λ ₀ (with λ ₀ being the wavelength of the lowest working frequency). The simulated results show that the proposed frequency beam scanning antenna achieves a wide scanning angle of 129° over a frequency range from 11.7 to 50 GHz (for |S ₁₁ | <; -10 dB) with an average gain level of 12.38 dBi. The good agreements between the simulated and measured results validate the proposed design.

In this paper, a band-pass filter based on the spoof surface plasmon polaritons (SSPPs) and CPW-based coupling structure is proposed. The design concept of the proposed band-pass filter is to use the SSPP structure and coplanar waveguide (CPW) based coupling structure for controlling the high cut-off frequency and filtering the low frequency wave, respectively, which means that the low and high cut-off frequencies of the band-pass filter can be independently controlled. Physical mechanism of the proposed band-pass filter is explained with the aid of dispersion curves, electric field distributions, and equivalent circuits. Moreover, parametric studies are conducted to analyze the effects of the key parameters on the controllable performance of the band-pass filter, which is useful for practical designs. Furthermore, in order to improve the high frequency performance, the split ring resonators (SRRs) are added to the structure. Simulation results show that the proposed band-pass filter achieves a bandwidth (for | S 11 |< -10 dB and | S 21 |> -1.6 dB) of 35.9% (7.31–10.51 GHz). Experimental results validate the proposed concept, and measured results are in good agreement with simulated ones, which indicate the proposed band-pass filter is believed to be significantly promising for further developing plasmonic functional devices at microwave frequencies.