Research Of Multilayer Tunable Devices Based On Spoof Surface Plasmon Polaritons

Surface plasmon polaritons(SPPs)are a special surface wave mode that propagate along interfaces of two media in optical frequency band.They have great potential in designs of superresolution imaging,high-precision sensors,and plasmonic circuits,due to the unique properties of near-field confinement,shorter operating wavelength and transmission cut-off in high frequency band.The periodic arrangement of unit structures could support certain surface mode in microwave that shows similar dispersive property with SPP,which is called the spoof surface plasmon polaritons(SSPPs).High-efficient excitement of SSPPs has been achieved by designing the matching structures.This thesis,mainly focuses on study of tunable functional devices based on SSPPs.Both a miniaturized tunable bandpass filter based on high-order mode of SSPP and a capacitance-loaded asymmetric beam-scanning leaky wave antenna were proposed.The main research contents were as follows:(1)A miniaturized tunable bandpass filter based on high-order SSPPs was designed.Periodic corrugated slots and cavity with the same contour were etched on the traditional SSPP unit.The cutoff frequency of SSPP modes was reduced by more than 50% without increasing its total dimension.The electric field and magnetic field along the novel units were analyzed.And the high-order mode could be directly excited from the microstrip line.The proposed bandpass filter shows great potential in miniaturization designs.(2)Capacitors were introduced on the novel bandpass filter to achieve tunable property.Two groups of capacitors were set to connect the corrugated grooves of the SSPP units to microstrip and background respectively.By changing the value of each group of capacitors,the central frequency and the working bandwidth of the bandpass filter could be controlled independently.The maximum increase of center frequency and working bandwidth were 31.2% and 69%,respectively.The measured results were consistent with the simulated ones.(3)A dual-layer asymmetric beam scanning leaky wave antenna based on SSPPs was proposed.The surface impedance of each layer could be controlled independently due to the isolation between layers of the multi-layer SSPP transmission networks.And the asymmetric beam scanning in each layer was obtained.Etching rectangular offset slots on the modulated units could significantly suppress the stopband effect on the wide side of leaky wave antenna.The maximum difference between the beam scanning angles in the upper and lower half space was 37 °.(4)A capacitor-loaded leaky wave antenna with asymmetric beam scanning was designed,which can realize asymmetric and tunable beam scanning.The modulation effect of capacitance on the surface impedance increased with the increase of groove depth.Capacitors were loaded on the units with deeper grooves to modulate the average surface impedance of the complex unit.When the average surface impedance was designed to be 650 Ω and 750 Ω,the maximum difference between beams angles with and without capacitors could reach 19° and 27°,respectively.When the modulated average surface impedance of both layer was different,the maximum capacitor-loaded angle difference between both layers could be 49°.