Research On Artificial Surface Plasmon Multi-frequency Filters

Surface Plasmon Polaritons(SPPs)is a surface wave propagating at the interface of metal and dielectric with good local confinement capabilities.However,they can only be effectively excited in light or higher frequency bands.With the proposal of Spoof Surface Plasmon Polaritons(SSPPs),SPPs can be extended to low frequency bands such as terahertz and microwaves which is achieved by the design of the metal surface geometry to control the cut-off frequency of the propagation of SSPPs.Microwave devices designed based on SSPPs have inherited the excellent characteristics of SSPPs,such as higher transmission performance,sub-wavelength structure size and so on.In microwave systems,filters are widely used.In particular,compared to single-frequency filters,multi-band filters are more flexible and efficient in practical applications,therefore,the design of multi-frequency filters has better practical significance.In this thesis,the design of multi-frequency filters is mainly based on SSPPs.Two/three-frequency filters are designed by using two different SSPPs waveguide structures: tapered groove and double-sided structure.And the specific research results are as follows:1.Multi-frequency filter based on tapered slot SSPPs waveguide.First,a low-pass filter with a wider bandwidth is designed based on the tapered slot SSPPs waveguide structure and the feed mode using coplanar waveguides.And it has an insertion loss of less than 3dB in the passband.Secondly,the passband can be divided into multiple frequency bands,which is obtained by the resonant stopband generated by the coupling between the symmetrical E-shaped resonator and the SSPPs waveguide.The E-shaped resonator has odd and even resonant two modes.The degradation of even mode resonance disappears,resulting in the original passband being divided into low-pass and band-pass,when the middle branch of the resonator reaches a certain value.One is the low-pass filter with 3dB insertion loss and 2.83 GHz cut-off frequency.The another is band pass filter with 4.2GHz working band width.And at the resonance center frequency has a higher suppression effect.The original low-pass filter becomes a three-band filter,including one low-pass filter and two band-pass filters.When both odd and even mode resonances exist.The cut-off frequency of the low-pass filter with 3dB insertion loss is 2.83 GHz.The first band-pass filter working band width is 1.43 GHz.The second band-pass filter working bandwidth is 2.7GHz.And at the center frequency of the odd-even mode resonance has a good suppression effect.Finally,an electrically tunable multi-frequency filter is realized by introducing a variable capacitance diode in the resonator.The simulation results show that the tunable bandwidth of the odd-mode resonance is 260 MHz,and the tunable bandwidth of the even-mode resonance is480 MHz.2.Multi-frequency filter based on double-sided SSPPs waveguide structure.First,a band-pass effect can be achieved by a dual-mode resonator,which formed by short-circuiting short-circuit stubs and open-circuit stubs on the waveguide transmission line.Secondly,with two band pass characteristics of a dual-frequency filter,which is combined with waveguide part and the transition structure and the micro strip feed part to design.The simulation results show that the first band pass filter with the 3dB insertion loss in 10.2GHz passband bandwidth.The second band pass filter with the 3dB insertion loss in 870 MHz passband bandwidth.And the isolation effect between the two passbands is very impressive,can reach52 dB suppression even.To make the filtering characteristics more intuitive by simulating the electric field distribution at the passband and out-of-band frequency points.Then,the simulation found that there will appear three passbands when the length of the short stub become lengthen.The first band-pass filter has 3dB insertion loss and the working bandwidth is 1.23 GHz.The second band pass filter has 3dB insertion loss and the working bandwidth is 560 MHz.The working bandwidth of the third band-pass filter with 3dB insertion loss is 450 MHz,and the maximum isolation suppression between each passband is62 dB,which has a better suppression effect.Finally,the fabrication and S-parameter test of the designed double/three-pass band filter structure.It is obvious that there is a good agreement between the measured and simulated S-parameters.