Research On The Terahertz Filter Based On Frequency Selective Surface

Based on the theoretical analysis and transmission characteristics of frequency selective surfaces(FSS)at Terahertz(THz)regime,two types of filter structures are proposed.One is a thermally tunable Terahertz bandstop filter based on the semiconductor InSb,the other is a dual-band Terahertz bandpass filter based on the combination of two resonant structures.The major work in the thesis is summarized as follows:(1)A frequency selective surface bandstop filter in the Terahertz spectrum regime based on the semiconductor InSb is presented.The resonant frequency of the filter is thermally tunable thanks to the dielectric constant properties of InSb.Meanwhile,the effects of geometrical parameters on the performance of the filter are analyzed by the finite-integral method and equivalent LMC circuit method,respectively.The results of the two methods show good agreement with each other.The resonant frequency can be dynamically tuned across a wide band of frequency from 0.91 THz to 1.28 THz in the temperature range from220 K to 350 K,and the transmission coefficient at the resonant frequency in the stopband can be effectively suppressed.Good incidence-angle stability of the transmission characteristics up to an oblique incidence angle of 30 o is demonstrated.The resonant frequency of the filter remains practically constant while the incidence angle changes in the region.The tunable FSS band-stop filter has the potential to be applied in THz wireless communication and sensing systems.(2)A dual-band bandpass filter in Terahertz spectral regime is presented based on frequency selective surface.The filter is composed of a two-dimensional periodic array of a composite structure consisting of a ring slot encircling an H-slot.With the resonant frequencies of the bandpass filter designed at 0.62 THz and 1.07 THz,simulations indicate that their 3-dB bandwidths are 200 GHz and 300 GHz,respectively,and good transmission characteristics are achieved within the two passbands.The electric field distribution on the surface confirms that the low resonant frequency is mainly produced by the ring slot while the high resonant frequency predominantly by the “H” slot.The two resonant frequencies can be adjusted independently via the structural parameters,and the insertion losses at them are both less than 0.45 dB.The low-loss mechanically tunable bandpass filter has the potential to be applied to the THz sensing and communication systems.