| With the rapid development of modern electronic warfare technology,the stealth technology of aircraft has received extensive attention from scholars at home and abroad.For the aircraft's own radar cross section(RCS)reduction,it is usually easy to achieve by modifying the shape and applying absorbing materials.However,the greatest contribution to the whole RCS of the aircraft is the antenna system installed on it.Therefore,it is particularly important to reduce the RCS of the antenna system.The reduction of antenna RCS is based on its radiation characteristics.In view of this topic,this thesis studies three new methods for realizing the antenna RCS reduction,and validates the correctness and feasibility of these methods through a series of simulation,processing and testing.1.A low RCS circularly polarized(CP)antenna based on AMCs has been designed.Firstly,two kinds of AMCs with 180 ° reflection phase difference are designed,and the two are arranged in a chessboard configuration.When radiated by the plane wave,the reflection waves of adjacent AMC regions can cancel each other out,and the RCS reduction can be achieved.At the same time,in order to realize the CP radiation,only the AMC1 in the diagonal direction has been feed with a 90° phase difference.Finally,the proposed antenna has an impedance bandwidth of 6.8GHz-9.6GHz,an axial ratio bandwidth of 7.7GHz-9.4GHz.And it radiates a left-hand circularly polarized(LHCP)wave in the operating frequency band with a maximum peak gain of 8.1d Bi.At the same time,compared with the traditional CP antenna,the proposed antenna has a low RCS property over a wideband of 8-18.5GHz under x-and y-polarized incident wave.2.A low RCS and high gain patch antenna based on holographic metasurface(HM)has been designed.It consists of three dielectric slabs,a 50 ? feed line is printed on the lowest slab to excite the antenna.The HM is printed on the middle slab and there is a square metal cavity in the center of this slab to receive the energy feed by the microstrip line.A square patch is printed at the center of the top slab working as the main radiator of the antenna.The energy in the metal cavity can not only excite the main radiator of the antenna,but also the HM,which can effectively increase the antenna radiation aperture,thus a relatively high gain as much as 10 d Bi is obtained,2.6d B higher than that of the conventional patch antenna.In addition,HM has the ability to transform the propagating wave(PW)into surface wave(SW).Therefore,the backscattering is greatly reduced,resulting in a low monostatic RCS.A wideband RCS reduction ranging from 5.5 GHz to 21.5 GHz have been achieved.It is also worth pointing out that the maximum RCS reduction is 21.64 d B around 8 GHz for both x-and y-polarized incident waves.3.In order to further expand the RCS reduction bandwidth of antenna by applying HM,a low RCS holographic antenna based on band pass absorber frequency selective surface(FSS)has been designed.The holographic antenna is excited by a monopole.The HM has the ability to transform the propagating wave(PW)into surface wave(SW).Therefore,the backscattering is greatly reduced,resulting in a low monostatic RCS.To further reduce the out-of-band RCS of the antenna,the band-pass FSS loaded with the lumped resistance is placed 9mm above the holographic antenna as a superstrate.The FSS is nearly all-pass in the working frequency band of the holographic antenna,which can ensure the radiation performances of the antenna.Outside the working frequency band of the antenna,the lump resistances can absorb the incident plane wave and convert it into heat energy,so that the out-of-band RCS of the proposed antenna can be effectively reduced.Simulation results show that the radiation performances of the proposed antenna have almost no change before and after loaisding FSS.Moreover,both in and out of band RCS reduction has been achieved under x-and y-polarized incident wave.It is worth mentioning that the average reduction is more than 10 d B over a wide frequency band. |
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