Corrugated metal surface with underlayer metal as ground is designed as spoof surface plasmons polaritons (SSPPs) structure in microwave frequencies. Efficient conversion from guided wave to SSPP is required for energy feeding into and signal extracting from such plasmonic structure. In this paper, first a high efficient transition design is presented by using gradient corrugated strip with underlayer metal as ground and by using the impedance matching theory. The SSPP wave is highly confined within the teeth part of the corrugated surface. By using this characteristic, then the simple wire-based metamaterial is added below the strip to manipulate the SSPP wave within the propagating band. Two aforementioned devices are designed and fabricated. The simulated and measured results on the scattering coefficients demonstrate the excellent conversion and excellent manipulating of SSPP transmitting. Such results have very important value to develop advanced plasmonic integrated circuits in the microwave frequencies.
In this paper, a direct synthesis approach is presented to realize high selectivity in-line topology filters with adjacent frequency-variant couplings (FVCs). By considering the annihilation of frequencyvariant elements during admittance matrix transformation for the first time, this paper provides a deterministic mechanism (no optimization is involved) that can generate FVCs between every two cascaded resonators. In consequence, a high selectivity filtering response where N-1 transmission zeros are implemented and independently controllable can be achieved for an Nth-order in-line network. As the foundation, a novel matrix process is detailed to obtain two adjacent FVCs inside of a 4th-order in-line network. The Nth-order prototype is then realized based on the process in an iterative manner. A synthesis example is illustrated in terms of the proposed approach step by step to show validity. Eventually, a 6th-order in-line band-pass filter, which contains adjacent FVCs in two pairs has been designed and fabricated via coaxial cavity structures. The synthesis results, EM simulation results, and tested results are well matched with each other, which reveals the effectiveness of the presented method during physical implementation. INDEX TERMS Filter synthesis, frequency-variant coupling, coupling matrix, transmission zero, microwave filters. The associate editor coordinating the review of this manuscript and approving it for publication was Yongle Wu. FIGURE 1. Schematic of (a) in-line prototypes discussed in this work (with adjacent frequency-variant couplings); (b) traditional cross-coupled prototypes; and (c) traditional extracted-pole prototypes. Note that solid line refers to traditional constant coupling, dashed line refers to frequency variant capacitance (slope), and the combination represents frequency-variant coupling in this work.
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