Research On Frequency Selective Surface Radome With Wideband Absorption

As stealth and detection technologies are developing toward a more diversified and intelligentized direction,it is impossible for conventional radomes to achieve all-around stealth.Therefore,more and more fields become more urgent for the design of new radomes with characteristic of comprehensive stealth.A bandpass frequency selective surface radome with special shape and performance is typically capable of isolating the detection from other antennas(radars)and it is critical for reduction of radar cross section(RCS)of antennas/radars.The conventional bandpass frequency selective surface radome allows electromagnetic waves to pass through at the operating frequency of antenna and reflects electromagnetic waves to other directions out of the passband.Thereby this type of radome can realize mono-static stealth while for bistatic or multistatic stealth,it will not work any more.In this thesis,we mainly study the absorptive frequency selective surface(AFSS)with wideband absorbing characteristics.It can achieve high transmission in the passband and realize broadband absorption out-of-band which will not affect the performance of the passband.Compared with the traditional reflection-type radomes,this AFSS radome can realize all-around stealth for the protected system.In this thesis,two types of AFSS are designed.Firstly,we design the circuit and structure of a AFSS with property of transmission at high frequency and broadband absorption at low frequency.By designing the metallized strip-type capacitor and inductor in parallel structure which has the resonant frequency at the passband,the absorbing structure will have no effect on the bandpass FSS.There is a passband at 16 GHz with the insertion loss of 0.29 dB.The absorption over 90%ranges from 8.5 to 14.5 GHz,with a relative bandwidth of 52.2%.The transmission and absorption properties are relatively stable under TE and TM polarization with incident angles from0~?to30~?.Besides,the graphene resistive film is applied instead of the lumped resistor which can realize an omnidirectional resistance with only one piece of square graphene in each unit cell.Thus the number of lumped elements is reduced,and the structure is more planarly integrated.The resistive film was fabricated by graphene mixed ink.We have measured the samples using a pair of focusing lens horn antennas and the measurement results agree well with the simulation results.Then,we design the circuit and structure of a AFSS with property of transmission at low frequency and broadband absorption at high frequency.In the first step,we change the pattern position of capacitor and inductor in parallel based on the prior AFSS structure.The new designed AFSS realizes a passband at 8.7 GHz and a broadband absorption from10~14 GHz(reflection lower than-10 dB).In the second step,we have improved the performance of stopband by loading an inductive path on the back of the substrate which also introduces a transmission zero on the left side of passband.In the third step,based on the previous AFSS structure,a transmission zero is added to the right side of the passband by designing a new bandpass FSS structure.After this,the final AFSS structure is determined.It has a passband at 8.43 GHz with the insertion loss of 0.13 dB and two transmission zeros at 6.32 GHz and 13.43 GHz respectively.The reflection less than-10dB is from 9.7 GHz to 14.8 GHz with a relative bandwidth of 41.6%.Transmission and absorption properties are relatively stable over incident angles of0~?~30~?under TE and TM polarization.