Study On The Miniaturized-Element Frequency Selective Surface And Its Applications

A two-dimensional periodic array of patch or aperture elements on a dielectric substrate is called a frequency selective surface(FSS)because of the frequency filtering property suggested by this structure.It has selective characterstics for electromagnetic waves with different operating frequencies,polarizations and angles of incidence and exhibits significant band-pass or band-reject filtering characterics when interacting with electromagnetic waves.It can used in radar radomes to reduce the radar cross section(RCS)of an array antenna,as a reflector to transmit and reflect electromagnetic waves in different frequency bands.Miniaturized-Element frequency selective surface(MEFSS)which can increase the number of FSS cells in a limited space and small area and approximate to an infinite FSS to obtain the ideal filtering characteristics and improve the sensitivity of the FSS response to the incident angle.The MEFSS has a lot of room for development in multi-band,ultraiwideband and controllable frequency selective surface designs.In this paper,we studied the basic theory,design principle and design method of MEFSS.We focused on the process of designing the frequency selective surface by combining the numerical analysis method and the equivalent circuit method,which laid a solid theoretical foundation for the design of the miniaturized frequency selective surface.The main work is to study how to reduce the size and reduce the profile of dual-band and ultra-wideband frequency selective surface elements.The main work and innovation of this paper are as follows:1.A dual-band miniaturized frequency selective surface based on complementary coupling and bending technology are proposed.Its equivalent circuit is given.According to the microwave filter theory,the electrical parameters of the equivalent circuit are calculated synthetically,and then the structural parameters of the frequency selective surface are calculated.The calidity and reliability of the proposed design method is verified by the theoretical simulation and test results.The results show that the proposed dual-band frequency selective surface has the characteristics of miniaturization and high angular stability.The unit size is 0.033λ ×0.033λ.Its resonant frequency is stable with the increase of the incident angle from 0 degree to 60 degrees.Then another type of ultra-miniaturized frequency selective surface is proposed by dislocation technology.The unit size is 0.01λ ×0.01λ,and the maximum angle of incidence up to 86 degrees.Compared to the previous litertures,the proposed design has a smaller unit size,ultra-low profile and high angle stability,which can be used to design the radome to solve the filter performance deterioration of the frequency selective surface due to bending deformation.2.In view of the inherent defects of frequency selective surface cell structure determining the resonant frequency characteristics and the limitations of traditional coupling and loading technology to achieve the frequency selective surface cell miniaturization,a dual-band miniaturized frequency selective surface based on lumped elements loading is proposed.The dual-band FSS with inductors loaded in the patch cell and the capacitors loaded in the aperture cell not only has the characterics of ultra-miniaturization,but also has the resonant frequency and band ratio flecible and controllable.Another type of dual-band MEFSS with controllable resonant frequency and polarization state is obtained by loading the PIN diodes.Therfore,the miniaturized frequency selective surface based on lumped elements has potential research value.3.Aiming at the problem that the high frequency band of dual-band frequency selective surface has poor angular stability and modal interaction null,a novel high selectivity low-profile dual-band band-pass miniaturized-element frequency selective surface is proposed to achieve stable angular response and tunable transmission zero.The proposed FSS is a three-layer structure consists of three metal layers separated from each other by two dielectric substrates.The equivalent circuit model of the FSS and its operating principle are presented and analyzed based on microwave filter theory.The prototype of the FSS is simulated,fabricated and measured,and its theoretical analysis,simulation and measurement results have a good agreement.The FSS achieves excellent angular stability and wide out of band rejection performance in the scope of incidence angles of 80 degrees.Compared with the other multilayered FSSs and 3-D FSSs proposed in previous works,its profile is lower,and the unit size is smaller.A transmission zero is introduced by etching slots on the edges of the middle metal layer to achieve superior frequency selectivity.By properly choosing the size and direction of the slots can change the transmission zero and polarization selectivity respectively.4.Aiming at the problem of large unit size and thich profile in the ultra-wideband bandstop frequency,a 2.5D ultra-wideband band-stop miniaturized frequency selective surface based on metallized via technology is presented.The principle of 2.5D MEFSS is analyzed in detain in combination with the equivalent circuit.And then the technology of metallized vias is used to design a ultra-wideband band-stop miniaturized frequency selective surface,which consists of a cross dipole unit,a ring unit and a metallized via square loop unit.The prototype of the FSS is simulated,fabricated and measured,and its theoretical analysis,simulation and measurement results have a good agreement.The results show that the proposed ultra-wideband band-stop MEFSS can cover the ultra-wideband range defined by FCC,and has the advantages of low profile,miniaturization and high angle stability.The unit size is 0.15λ ×0.15λ,and the maximum incident angle can reach to 60 degrees.The-10 dB percentage bandwidth is 161.9%.The-10 dB percentage bandwidth will increased to 231.5% when cascading technology is used and the-20 dB percentage bandwidth is 185.4%.A UWB antenna is presented with the 2.5D ultra-wideband band-stop frequency selectives surface as the reflector.The gain of the UWB antenna has successfully increased without affecting the reflection coefficient of the UWB antenna.The FSS reflector has the function of increasing the antenna front-to –back ratio and improving the antenna efficiency.The proposed ultra-wideband band-stop miniaturization frequency selective surface can be used to improve the radiation performance of an antenna in the ultra-wideband range.