Research On Miniaturization And Transmission Characteristics Of Spoof Surface Plasmon Polaritons In Microwave Region

Spoof Surface Plasmon Polaritons(SSPPs)are approximate electromagnetic modes of surface plasmons polaritons(SPPs)in the microwave region,which inherit the near-field enhancement,sub-wavelength confinement and slow-wave characteristics of surface plasmons polaritons.These characteristics can greatly improve the performance of SSPPs-based microwave devices.However,due to the large size of existing SSPPs-based microwave devices,and most of them are limited by the inherent low-pass characteristics of SSPPs,the practical application of SSPPs is limited.Therefore,this paper studies the equivalent circuit of SSPPs,the miniature transition of traditional planar transmission lines to SSPPs,the band-pass and adjustable double-passband transmission characteristics.Specific research work includes:(1)The equivalent circuit topology of a typical SSPPs unit is established.A simple equivalent circuit calculation formula is used to propose an equivalent circuit model with high precision.The basic equivalent circuit model is provided for the SSPPs unit with load and variable capacitance.Based on the two-conductor SSPPs unit impedance extraction method,the periodic element impedance is calculated.The impedance value is used to adjust the transition section impedances.The wave vector matching overcomes the shortcomings of the low-band reflection coefficient of the traditional low-pass transmission line,and the miniaturization of the transition is realized.Furthermore,a coplanar waveguide interdigitated H-type SSPPs unit has been proposed,and the transmission line based on the unit has been miniaturized in both the horizontal and vertical directions.(2)Based on the design method of the microstrip short-circuit branch high-pass filter,the geometry of the high-pass filter is calculated,and it is combined with the SSPPs transmission line to obtain the band-pass transmission line with high and low cutoff frequency separately controlled by SSPPs and short-circuit branches.Based on the microstrip H-type SSPPs unit loaded with the interdigitated structure,the dispersion curve of the SSPPs is improved,and the band-pass transmission line based on the loaded interdigitated structure is also realized.(3)Based on the microstrip H-type SSPPs equivalent circuit of the loaded chip capacitor,the cut-off frequency of the elementary fundamental mode is calculated,and the cut-off frequency of the high-order mode is calculated by using the eigenmode.Combined with the miniaturized transition design of Chapter 3,a double passband transmission line is realized.Based on the double-passband transmission line design method,the cut-off frequency of the fundamental mode of the SSPPs unit with variable capacitance is calculated.The actual equivalent circuit of the variable capacitor is used to adjust the dispersion curve of the SSPPs of the loaded patch and the variable capacitor.Combined with the DC bias,an adjustable double-pass transmission line is realized.The microstrip H-type SSPPs miniaturized transition section transmission line and the improved SSPPs transmission line with short-circuit branch and interdigitated structure are processed and manufactured.The test results are in good agreement with the theoretical simulation.The work of this paper further promotes the practical application of microwave transmission lines based on SSPPs.