Computation Of Antenna Isolation Based On Spherical Wave Expansion

With the rapid development of wireless communication,in order to achieve faster transmission rate,larger channel capacity,or meet the transmission requirements of different frequency bands,more and more antennas are carried on the same platform.At this time,the electromagnetic interference(EMI)generated by spatial coupling between antennas will degrade the performance of each system,or even make it unable to work normally.In this paper,mutual impedance is used to describe the mutual coupling between antennas,and vector spherical harmonic transform is used to accurately calculate the mutual impedance.The main research contents are as follows: 1.An ultra-high order spherical harmonic transformation algorithm is proposed.This method uses a normalization strategy to calculate the ultra-high order associated Legendre functions(ALFs),which solves the numerical overflow problem of ALFs,and use the fast Fourier transform(FFT)to accelerate,so that the near-field-to-far-field transformation(NFFFT)of the antenna with an electrically large size can be carried out efficiently.2.A fast algorithm is proposed to obtain the mutual impedance through the response integral of the near-region electric field and magnetic field of the two antennas according to the reciprocity theorem.Firstly,the tangential electric field on the surrounding sphere near each pair of antennas is measured or simulated,and then the spherical harmonic coefficient of each pair of antennas is obtained by using the spherical harmonic transformation method.The electric field and magnetic field of the first antenna on the sphere surrounding the second antenna are obtained by interpolation method.Finally,the reaction integral is calculated to obtain the mutual impedance.This method is more accurate than the existing mutual impedance fast algorithm.Because the latter adopts plane wave expansion to analyze the antenna's near field,the litters in the near region are ignored,making the result of reaction integral inaccurate.If the mutual impedance between two antennas is optimized using computational electromagnetics(e.g.However,the method in this paper only needs to measure or simulate each pair of antennas once,and then the mutual impedance of the two antennas at any relative position or Angle is completely analyzed by a fast method.Therefore,this method has a good prospect of engineering application.