| With the rapid development of science and technology,the traditional weapon systems are increasingly threatened in combat.In order to improve the survivability and combat capability of weapon systems,stealth technology has attracted the attention of the world.The Radar Cross Section(RCS)is the most critical indicator in stealth technology.The traditional RCS reduction methods include modifying the shape and coating radar absorbing materials.The most important RCS contributor is antenna,so more and more scholars put their energy into the study on how to reduce antenna RCS.Aiming at this topic,this thesis studies four methods to reduce antenna RCS,and uses a series of simulations,fabrications and tests to validate these methods.1.An in-band low RCS microstrip array antenna based on phase-control metasurface is designed.As the size of the phase-control metasurface changes,it will have different phase adjustments to the incident electromagnetic wave.Two phase control metasurface with a 90° reflection phase difference are arranged in a checkerboard and loaded above the microstrip array antenna.Since the electromagnetic wave transmission frequency band of the phase control metasurface is the same as the working frequency band of the microstrip array antenna,the electromagnetic wave radiated by the antenna can pass through the phase control metasurface with low lose.When the electromagnetic wave is incident,the metal of the microstrip array antenna will totally reflect it,so the incident electromagnetic wave passes through the metasurface again and forms a reflected wave with a phase difference of 180°±37° when passing through the phase-control metasurface of different size.Therefore,the microstrip array antenna can achieve in-band RCS reduction.In the entire working frequency band,the RCS average reduction value of the x-polarization and the y-polarization is 10 d B and 9.1d B.In order to further reduce the in-band RCS of the above array antenna,a polarization-dependent absorbing material is designed and loaded on the microstrip array antenna.The absorbing material absorbs the electromagnetic wave through electric resonance and converts it into heat energy to reduce the RCS of the antenna.Since the absorbing material is polarization dependent and will not have any effect on the same polarization,the antenna can work normally.Finally,in the whole working frequency band of the antenna,the RCS reduction value of both the x-polarization and the y-polarization is greater than 10 d B.The gain loses 0.1d B at the frequency point.2.A low RCS array antenna based on the reflected wave path difference is designed.When electromagnetic waves are incident on the microstrip antenna units of different heights,a reflection phase difference will occur.A reasonable height difference makes the reflection phase difference by 180°±37°.The antenna units of the two heights are arranged on a checkerboard to realize the in-band RCS reduction of the microstrip antenna.Antenna units with different heights will have radiation phase compensation to ensure that the radiation performance of the antenna will not be affected.The working frequency band of this antenna is 5.2GHz-5.8GHz.Significant reductions have been achieved in both the x-polarization and the y-polarization over the entire operating frequency band.The maximum in-band RCS reduction for x-polarization and y-polarization is 24.47 d B and 19.55 d B,respectively.3.A low RCS array antenna based on Absorb Frequency Selective Surface(AFSS)is designed.Firstly,an in-band low RCS microstrip array antenna operating at 5.7GHz is designed by using reflected wave path difference.In order to further expand the RCS reduction bandwidth of the antenna,the AFSS is loaded above the antenna.When the transmission frequency of the AFSS is consistent with the working frequency of the antenna,the radiation performance of the antenna will not be affected.The lumped resistance on the AFSS is used to realize its wave-absorbing function.The electromagnetic waves incident outside the passband of the AFSS will be absorbed by the lumped resistance and converted into heat energy to realize the antenna RCS reduction.When x-polarized electromagnetic waves are incident,AFSS expands the antenna RCS reduced frequency band from 4GHz-14 GHz to 3GHz-18 GHz,and when y-polarized waves are incident,AFSS expands the antenna RCS reduced frequency band from 4GHz-12 GHz to 3GHz-18 GHz. |
