Study Of High Impedance Surfaces Used For Controlling Radar Cross Sections Of Antennas

In modern wars with complicated electromagnetic environment, the stealthperformances of weapon platform and aircraft directly determine their battlefieldsurvival probability. With the development of Radar Absorbing materials (RAM),Frequency Selective Surfaces (FSS) and other artificial materials, the Radar CrossSection (RCS) of platforms has been controlled at a low level. As one of the mostimportant components of weapon system, antennas become the main factor of radioscattering. The scattering of antennas mainly determine the platform’s stealthperformance. Therefore, effective methods to control the antennas’ RCS have becomeone of the most urgent problems in stealth technique. Nowadays most shape techniquesand material techniques about RCS reduction of antenna have limitations. Thisdissertation focuses on the in-band RCS control method useing high impedance surfaces.The author’s major contributions are outlined as follows:1. The equivalent circuit model of high impedance surfaces is analyzed. Themechanism of the surface wave band-gap and reflection phase band-gap is given. Thedispersion energy band method and the direct transmission method are used to analyzethe surface wave band-gap, and the infinite period model method is used to analyzereflection phase band-gap. The measurement methods of both band-gaps are proposed.With the reflection phase band-gap of HIS, the HIS can be used to reduce the in-bandRCS of antenna.2. The effects of five basic configuration parameters of square HIS unit on surfacewave band-gap and reflection phase band-gap are analyzed. The five parameters includemetal patch width, gap width, metal via radius, thickness of dielectric board andpermittivity of dielectric board. The results can be used in the HIS structure design.3. The differences between the finite period and infinite period structure of HIS isanalyzed. The finite period structure of HIS is fabricated on microstrip antenna. Thesimulated and measured results show that the in-band RCS is effectively reduced byusing HIS. When HIS structure is fabricated on the top surface of the microstrip antenna,the RCS of antenna at working frequency is reduced by7.71dB, and the in-band RCS isreduced by at least2.5dB. Comparing with the original antenna, the proposed antennahas similar radiation characteristic.4. HIS structure is used in dual-band antenna and array to reduce the in-band RCS. By cascading two different sizes of HIS structure, dual reflection phase band-gaps arerealized. When the cascading HIS structure is fabricated on dual frequency microstripantenna with U-shape, the simulation and measured results show that being comparedwith the original antenna the in-band RCS of the U-shape dual-band antenna is reducedby16.81dB at lower working frequency and5.78dB at higher working frequency. Thefinite period HIS elements with high permittivity dielectric board are fabricated onmicrostrip array, and the measured results show that the in-band RCS reduced by atleast5dB. The effectivity of the proposed method is proved. Meanwhile, the radiationcharacteristic of antenna can be kept by changing parameters of HIS structure.5. In order to research the probability of the applications of HIS in the RCSreduction of different type antennas, the miniaturization of HIS structure is studied. Twomethods of realize miniaturized structure is proposed. The method of dielectric coveringchanges the band-gap properties by covering dielectric board on the top of HIS, and thepermittivity of covering dielectric is the same as HIS structure. The other methodrealized miniaturized structure by interdigital structure. The effect of configurationparameters of interdigital HIS structure on reflection phase band-gap is analyzed.Interdigital HIS structure is combined with PEC structure, the measured results provethe method’s effectiveness on RCS reduction.