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A micromachined 385 GHz rectangular waveguide cavity bandpass filter is presented. The proposed filter is fabricated using deep reactive ion etching on silicon substrate, with sputtered gold inner surface metallization. The vector network analyzer measured results show the lowest insertion loss is about 2.7 dB with a 15 GHz bandwidth. Effects of micro-electro-mechanical systems process on the filter's performance are discussed in detail.Index Terms-Bandpass filter (BPF), micro-electro-mechanical systems (MEMS), rectangular waveguide, terahertz (THz).

In this paper, we numerically and experimentally demonstrate a substrate integrated plasmonic waveguide (SIPW) concept and its application in microwave bandpass filters. This SIPW consists of double arrays of slots etched on the top and bottom metal layers of a substrate integrated waveguide (SIW) to support spoof surface plasmon polariton (SSPP) modes with low and high cutoff frequencies. The simulated results show that by tuning the parameters of the SIPW's unit cell, the dispersion characteristics can be engineered at will. Then, we propose a sharp roll-off microwave bandpass filter based on this SIPW. This filter has a passband from 7.5 to 13.0 GHz with high return loss and low insertion loss. Furthermore, to demonstrate the independent tuning of the passband of the filter, we also design two microwave bandpass filters with passbands of 9.2-13.0 GHz and 7.5-10.5 GHz by decreasing the distance between two rows of via holes and increasing the slot length, respectively. Finally, to experimentally validate the filter designs, we fabricate and measure three prototypes and find that the experimental results are in excellent agreement with the simulations. This SIPW concept may have extensive potential applications in the development of various plasmonic integrated functional devices and circuits. INDEX TERMS Spoof surface plasmon polaritons, substrate integrated plasmonic waveguide, bandpass filter.

In this paper, we introduce the fractal geometry into the spoof surface plasmon polariton (SSPP) waveguide and splitter design. We propose a novel SSPP waveguide consisting of periodic corrugated Greek-cross fractal units (GCFUs) connected to a microstrip line. The generation process of periodic corrugated GCFUs is described and the dispersion characteristics are studied. We find we can engineer the property of the waveguide at will by tuning the parameters of the GCFU. To validate the proposed design, a wideband lowpass filter based on double-sided DCFUs with ultra-sharp roll-offs is fabricated and tested. Based on this waveguide concept, we design a wideband Y-splitter including an SSPP waveguide with double-sided GCFUs and two SSPP waveguide branches with single-sided GCFUs. To improve isolations and reduce the reflections between output ports of the Y-splitter, a 100 Ω resistor is loaded in the middle of two symmetrical branches to construct Wilkinson splitter to equally and efficiently split the energy of the SSPPs into two parts. The simulated and measured results show that the SSPP splitter possesses excellent performance in a passband of 1.5–4.0 GHz with low insertion loss (S21, S31 > −4 dB), high reflection loss (S11, S22, S33 < −10 dB), and high isolation (S32 < −10 dB). This work may open up a new door for the development of various plasmonic integrated functional devices.

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