| With the rapid development of avionics and radar detection technology,the environment of modern battlefield is becoming more and more complex.New radar,guidance system and various anti reconnaissance equipment put forward higher requirement for stealth technology.Antenna is an important part of radar cross section of the target system,and it is also the main contributor to the overall RCS of the system,so RCS Reduction of antenna has an important impact on reducing the overall RCS of the system.There are several methods of antenna radar cross section control,which are antenna modification technology,absorbing material loading technology and cancellation technology.In this paper,new metamaterial and antenna are studied.1.The new type of metamaterial absorber is designed,which can enhance the absorption bandwidth by superposing two layers of absorbers working in different frequency bands.The upper absorbing structure works in the low frequency band,the loss layer is composed of metal square ring structure loaded with resistor,and the fractal curve is introduced into the ring to make the whole structure miniaturized,which is used to match the unit size of the lower structure;the lower absorbing structure works in the high frequency band,which is the combination of split ring resonator,resonant branch and patch resistor,and is realized by constructing a variety of resonant forms to achieve wideband absorption.Finally,the two-layer miniaturized absorbing structure can achieve the absorption in the range of 2.79GHz-17.23GHz,and its profile height is only 0.0846?0,and the unit size is only 0.0837?0.The RCS Reduction in a wide frequency band of 2GHz-20GHz can be achieved by loading the designed absorber around the microstrip antenna.2.The two kinds of low RCS circularly polarized antennas are designed based on defected ground and fractal structure.The first one is using Koch fractal and tree shaped slot lines on the antenna ground that broad the working bandwidth of antenna.Moreover,the RCS of the antenna is reduced due to the change of the ground.Compared with the reference antenna,the 3d B axial ratio bandwidth of the designed antenna the circular polarization bandwidth and matching bandwidth of the antenna are further expanded.is increased from0.45%to 0.9%,and it is within the wide band range RCS Reduction is realized.In addition,a tree structure with fractal form is designed,which is loaded around the antenna ground.Combined with the Koch fractal slot in the center of the ground,by introducing a new resonance point,matching bandwidth is increased from 2.06%to 8.7%and the circular polarization bandwidth is increased from 0.45%to 2.83%,the circular polarization bandwidth and matching bandwidth of the antenna are further expanded,and the RCS of the antenna is also effectively controlled.3.Based on the absorber and frequency selective surface,the metamaterial with multiple functions is designed.Firstly,design the absorber with low profile characteristics,the split ring itself,the gap between the rings and the lumped resistance are combined to realize the broadband absorption of the whole structure.Because the four split rings can be regarded as a whole structure,the miniaturization design of the structure is also completed.The absorptivity of the structure is over 90%in the range of 6.38GHz-14.44GHz,and the profile height is 0.063?0.Then,the miniaturized cross shaped FSS is placed at the bottom of the ultra-thin absorber,by adjusting cross arm length to complete the transformation from linear polarization to circular polarization.The designed structure can convert linear polarization transmission wave to circular polarization in the range of 2.44GHz-2.56GHz,and the incident wave absorption in the range of 6.82GHz-13.86 GHz.In addition,the Fabry Perot resonator cavity is formed by combining the designed absorbing structure with the partially reflective surface and the microstrip antenna.The antenna gain is improved by multiple reflections of the partial reflector and the antenna floor,and the upper absorbing structure achieves low RCS characteristics.The gain of the designed antenna has been significantly improved in the working frequency band of 12.62GHz-13.07GHz.The gain of the designed antenna has been increased by 6.5d B at 12.7GHz,and the RCS has been significantly reduced in 4GHz-11GHz. |
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