| The airborne radome is an electromagnetic functional component located in front of the aircraft to protect the radar system from the damage of the outside environment.In order to meet the requirement of modem aircraft,the airborne radome should be transparent in the pass-band and reflective/absorptive out of the pass-band.The frequency selective surface(FSS)radome has been proved to be the best choice.However,due to the complex structure of FSS radome,it is more difficult to obtain the mapping relationship between the structural parameters and the electrical property.The lacking of the mapping relationship poses a challenge to the high-performance design of the FSS radome.Meanwhile,the FSS radome usually adopts a streamlined shape,which leads to a large range of incident angle.The enabling characteristics require that the transmission performance of the radome wall should be stable at large incident angle,which increases the design difficulty.In addition,due to the lack of rapid analysis algorithm for electrical property,it is difficult to evaluate the electrical performance during the design process to optimize the design scheme.The electrical performance is only evaluated at the final stage with commercial software or experiments,which is not conducive to rapid development and performance improvement of FSS radome.Therefore,how to design FSS radome rapidly on the basis of high-performance requirements is a key problem to be solved.The solution of this problem is of great significance to the performance improvement and popularization of FSS radome and the development of related weapons and equipment.To solve the aforementioned problem,the analysis methods for FSS are investigated firstly.Then,the design method for FSS array and strategy for improving the angular stability of transmission performance have been studied.Based on these researches,the design method for FSS radome wall is formed.With the designed radome wall,electrical performance has been investigated by the modified Plane Wave Spectrum-Surface Integration(PWS-SI)algorithm.Then,the radome wall can be optimized with the analysis results.As a result,the FSS radome can be achieved rapidly.The main research contents are as follows:(1)The analysis method for FSS.This paper expounds the working mechanism of FSS,firstly.Then,the equivalent circuit method for FSS analysis has been studied.The modeling strategy and equivalent circuit parameter extraction have been investigated to analysis FSS rapidly.Subsequently,the Finite-Difference Time-Domain(FDTD)method has been studied.With the periodic boundary condition and absorptive boundary condition,performance of the FSS array has been analyzed by the FDTD method with high accuracy.(2)To solve the design problem of FSS,design method based on the combination of binary particle swarm optimization(BPSO)algorithm and pixel-overlap technique and design method based on equivalent circuit model have been proposed.In the first method,the structure of FSS element is modeled by;"0/1"codes and the optimized structure is obtained by BPSO algorithm.With the application of pixel-overlap technique,lattice points within the FSS structure can be avoided.In the second method,the relationship between the equivalent circuit parameters and transmission performance has been established via the equivalent circuit model,and the structural parameters are determined by the curve-fitting teclhnique.Performance of the two methods has been verified by experiments and the experimental results show that the second method is suitable for rapid FSS design.(3)Strategy for stabilizing the transmission performance.The angular stable transmission performance is obtained by improving the angular stability of resonant frequency and bandwidth simultaneously.To improve the angular stability of resonant frequency,various miniaturized FSSs have been designed by tortuous structure and loading lumped reactive components.Also,the bandwidth angular stability is improved by bonding composite structure composed of dielectric layers of high and low relative permittivity.(4)The equivalent circuit model based design method for FSS array and the strategy for stabilizing the transmission performance have been combined to form the design method for FSS radome wall.In this paper,design method for single band/dual-band FSS radome wall and design method for FSS radome wall with fast roll-off and wide out-of-band rejection characteristics have been proposed.The experimental results show that FSS radome wall designed by these methods can provide a pass-band operating at lOGHz with a-3dB bandwidth of 1.2GHz within the stopband ranging from lGHz to 40GHz.And the bandwidths of the transition bands between the pass-band and stop-band are only 0.26GHz and 0.6GHz.Also.Performance of the designed FSS radome wall is stable at 60°.(5)To solve the problem of electrical performance analysis of FSS radome,a modified PWS-SI algoritFhm has been proposed.In the method,transmission coefficients of the radome at interpolation points are calculated by FDTD algorithm,then,transmission coefficient at any incident angle can be determined with cubic interpolation.As a result,the PWS-SI algorithm can be applied to analyze FSS radome rapidly.Finally,the influence of the structural parameter variations of the designed radome wall on the electrical performance has been investigated by the modified PWS-SI algorithm if the specific radome profile equation is provided.With the analysis results,the radome wall can be optimized again to meet the requirements of electrical performance.As a result,with the proposed design strategy,the high-performance FSS radome can be achieved rapidly. |
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