The Research Of Terahertz FSS Bandpass Filters

With the rapid development of terahertz(THz) technology, many potential applications such as biotechnology, medical imaging, THz communications, and plasma diagnostics have been realized. In these applications, it is vital and necessary to manufacture high quality factor THz filter. Frequency selective surface(FSS) is a two-dimensional planar structure, which is composed of one or more metallization patterns and supported by the substrate. FSS can make an effective response to the terahertz wave by changing its structure, so FSS structure has broad application prospects in terahertz technology. In this thesis, FSS structure is in-depth studied, and FSS bandpass filters are designed which show perfect bandpass characters in the terahertz communication window ?. The research results have certain actual application value in the terahertz technology.The FSS structure units are classified first. Then the FSS structure is theoretically analyzed by using spectral domain method and equivalent circuit. Meanwhile, that how the grating lobe appears which will not only cause the consumption of energy but also cause the deterioration of filter performance is discussed. The series of analysis establish a theoretical foundation for the design of terahertz bandpass filters.Next, the filtering characteristics of slot FSS structures are seriously researched and studied. The various factors that influence the filters' performance include geometric parameters, metal materials, substrate, arrangement mode and single layer cascade. At the same time, polarization and the angle of incidence are taken fully into account. The results and conclusions provide references for the design of terahertz bandpass filters.Aiming at improving the characteristics of the circle slot FSS bandpass filter, a composite slot FSS bandpass filter based on tripe element is designed which shows bandpass filter characters in the terahertz communication window ? and the center frequency is 338 GHz. Results show that the comprehensive performance of the composite slot filter is better than the circle slot one. The 3dB bandwidth reaches 69.5GHz, the return loss is less than-13.46 dB, the maximum insertion loss in-band reaches 0.45 dB and the ripple is as low as 0.1dB. The filter shows stable filtering properties at different polarization wave and the same polarized wave at different incident angles in the meantime. So it can be effectively used in the field of terahertz atmosphere communication. In order to gain higher transmission rate in the central frequency, a new composite slot FSS bandpass filter is presented. The filter is achieved by removing the four corners of the metal layer, changing the current distribution on the unit's surface. As a result, the 3dB bandwidth is 71.02 GHz and the transmission rate in the central frequency reaches 0.948. Furthermore, a square circle slot FSS bandpass filter is designed to protect the metal layer by loading substrate s on both sides of the FSS structure. The filter realizes wideband and stable filtering properties, the 3d B bandwidth is 73.25 GHz and the return as low as-14.69 dB.Last, the processing technology of the designed terahertz FSS bandpass filters is effectively analyzed, demonstrating the feasibility and providing evidence for the physical preparation and production.In conclusion, the bandpass filters based on FSS are designed in this thesis have good performances for terahertz wireless communication system.