Design Of Microwave Passive Circuits Based On Artificial Surface Plasmons

In the optical frequency band,surface plasmon polaritons(SPPs)are electromagnetic waves excited by the coupling of incident electromagnetic waves and free electrons in the metal surface,which propagates along the interface between the metal and the dielectric.In addition,the energy decays exponentially in the direction perpendicular to the interface.For the metallic negative permittivity in the optical frequency band,the SPPs can be tightly bounded to the interface between the metal and the dielectric.However,due to the perfect electric conductors(PEC)of the metal in the microwave and terahertz bands,SPPs cannot be directly transmitted,there are no natural SPPs mode in this low frequency band.In order to achieve the propagation of SPPs in the microwave and terahertz bands,the researchers proposed a structure in which periodic sub-wavelength grooves or holes are etched on the metal surface,and this structure is called spoof surface plasmon polaritons(SSPPs).Based on the study of predecessor,we make a systemcial research about the application of SSPPs in aspects of the passive circuits.This paper has carried out mainly the following aspects of work:1.A novel balanced bandpass filter based on double-layer SSPPs is designed.Firstly,a power divider based on SSPPs is proposed,which consists of a double-layer SSPPs transmission structure based on double-sided parallel strip line(DSPSL)and a single-layer SSPPs transmission structure.Then,a four-port differential bandpass filter based on doublelayer SSPPs is proposed,which consists of a double-layer SSPPs filtering waveguide and a single-layer SSPPs waveguide with under-layer metal ground to realize bandpass filtering of differential mode signals.Moreover,a 180° inverter combined with metal via holes and DSPSL is also loaded in the differential filter to suppress the common mode signal in a wider frequency band.2.A novel bandpass leaky-wave antenna based on double-layer SSPPs is designed.The radiating element is an inverted trapezoid and is symmetrically distributed vertically.The whole antenna is composed of a plurality of sets of radiating elements closely arranged.With a dense arrangement of the radiating elements,high-order spatial harmonics are restrained to ensure the single beam radiation,and the structure of the radiating elements arranged by periodicity has a dispersion relationship similar to that of SSPPs.In addition,the bandpass filtering function is realized by loading shorted branch with metal via-holes on the microstrip transmission line,which can introduce transmission zero points.3.A novel filtering antenna based on double-layer SSPPs is designed.Firstly,a filter waveguide structure based on double-layer SSPPs with shorted branches is proposed.And a metal ground is loaded at the end of the waveguide for mode conversion and impedance matching,so that the signal can be transmitted to the free space.Then through further improvement,a filter waveguide structure based on double-layer SSPPs with shorted branches and U-shaped branches is proposed.The filter waveguide can achieve better filtering performance and selectivity,also,the zero point can be adjusted according to the changes of different parameters in the waveguide.Finally,a filter antenna with better bandpass effect is realized by loading a metal ground structure at the end of the waveguide.