Frequency Selective Surface Based On Resonant Cavity

Frequency selective surfaces with wonderful spatial filtering action have been a hotspot in recently years.FSS can be widely applied in several fields,for example,it can be used as a polarizer in optical field as well as used as a radome in radar system to control the radar cross section.With the extending of the applied range of FSSs,the demand of its steep roll-off,low insertion loss,low cross-polarization and stability at oblique incidence become higher and higher.According to the requirements mentioned above,this dissertation proposes a series of FSSs structures based on cavities with a hybrid boundary.A broader bandwidth and a steeper roll-off at sides of the passband can be easily achieved with the proposed FSSs by exciting resonances in hybrid boundary condition(HBC)cavities and properly merging them with the resonances of the slots.The main contributions of this dissertation are listed as follows.Firstly,it can be seen that cavities with high Q have been increasingly applied in the design of FSSs.Therefore,this dissertation analyzes the resonant modes of FSS in very great detail by making it equivalent to finite-size parallel plate.The expressions of cavities' resonant frequency with different boundary condtions have been given after a series of derivation procedures.Furthermore,a 2-D solver is used to verify the accuracy of these expressions.It is worthy to mention that the expressions and mode field distributions given in this dissertation lay a sound foundation for the designs of arbitrary FSSs based on cavity.Then,three novel bandpass FSSs based on HBC cavities have been proposed in this dissertation,including the FSS with a steep roll-off at one side of the passband,the FSS based on shorting vias and the dual passband FSS.In these FSSs structures,a steeper roll-off at sides of the passband can be easily achieved by exciting resonances in HBC cavities and properly merging them with the resonance of the rectangular slots.Finally,a novel low cross-polarization bandpass FSS with low passband ripples and a steep roll-off at both sides of the passband is proposed.The FSS is fabricated and its near-and far-field performances are measured which are in good agreements with the simulation prediction.The characteristics,including a steep roll-off,low passband ripples,a low cross-polarization,and stability at oblique incidence angles,are verified by the measurement.Also,we think that the proposed FSS can be used as an add-on screen to reduce the cross-polarization levels in polarization-diverse radar systems.Therefore,the near-field setup is used to exam the effect of the FSS sample on the transmit antenna.The measurement results show that about 18dB reduction of the antenna cross-polarization is achieved by adding the FSS screen.The methods used in this dissertation provide certatin reference significance for subsequent FSSs'designs.Some achievements of the proposed FSS have been published on IEEE Trans.Antennas Propagat.