Research On 3D Frequency Selective Surface Based On Multi-layer PCB

As a kind of spatial filter,a frequency selective surface is widely used in antenna and microwave systems,has selective filtering characteristic for electromagnetic wave with different frequencies,polarizations and incident angles.Traditional 2D FSS designs can only provide limited resonant mode,which show poor filtering performance.Therefore,it is more and more difficult for a 2D FSS to meet modern microwave and communication systems.Recently,a new class of 3D frequency selective surfaces,by constructing multiple resonators in each 3D-cavity based element,have been reported to achieved high performance.However,the most of 3D structures are their complicated topologies,which will definitely increase the implementation difficulties when applying in high frequency applications.In this thesis,the operating principle and equivalent circuit of a class of high performance 3D FSSs are investigated deeply.Based on the traditional multi-layer printed circuit technology,the designed high performance 3D FSSs are modified and fabricated,which can greatly reduce the fabrication tolerance.With this method,the applications of 3D FSSs can then be broadened.The detailed research contents of this thesis are concluded as follows:(1)In this chapter,a brief analysis of the traditional 2D FSS operating mechanism and the equivalent circuit are introduced.Taking the square ring array as an example,the classical FSS equivalent circuit parameter extraction method is explained.Based on this,the generalized equivalent circuit model of 3D FSS is described.By taking a microstrip line array as an example,a new method of extracting the equivalent circuit parameters of 3D FSS are studied.(2)In this chapter,a novel 3D frequency selective structure(FSS),exhibiting bandpass filtering response with high frequency selectivity,is presented.In each unit cell,multiple resonators are constructed to provide multiple transmission zeros/poles.By establishing an equivalent circuit model,it is obtained that the transmission poles in the passband are produced by a short-circuited resonator and an open-circuited resonator,and the transmission zeros close to the passband are attributed to the fundamental and spurious resonant frequencies of another short-circuited resonator.To implement it in high frequencies,multilayer printed circuit board technology is introduced,where several replacements are carried out.The measured results show good agreement with simulations.Furthermore,the proposed FSS exhibits stable performance with incident angles increased from 0 to 50°.(3)In this chapter,a multilayer bandpass frequency selective structure(FSS)with miniaturized unit cell and ultra wide stopband is presented.The proposed structure is made up a multilayer printed circuit board with a number of via holes,which can construct stepped-impedance resonators.The operating principle is briefly explained by analyzing the electric field distributions and parametric studies.Simulation results indicate that the size and thickness of a unit cell are 0.07?0×0.05?0×0.1?0 and the bandwidth of the upper stopband is from 7.5GHz to 33.5GHz(|S21| below-20 dB).(4)In this chapter,a novel tri-band frequency selective surface(FSS)is proposed by using multi-layer printed circuit boards with a number of via holes.Three separate propagation paths with two stepped-impedance resonators(SIRs)and a uniform-impedance resonator(UIR)are constructed in each unit cell of the proposed FSS,thus leading to tri-band bandpass performance.The lowest and the middle frequency bands are achieved by two SIRs,respectively,and the highest frequency band is obtained by the resonance of the UIR.Therefore,these three passbands can be realized independently,which can increase the design freedom.The operating principle is explained by analysing the electric field distributions.To verify the design concept,a prototype of the proposed FSS is simulated and tested.Measured results show that the FSS features stable tri-band performance under a large variation of incident angle.