Use of computational electromagnetics to enhance the accuracy and efficiency of antenna pattern measurements

The objective of this paper is to illustrate that computational electromagnetics can be used very effectively to improve the accuracy and efficiency of antenna pattern measurements. This is accomplished by moving a single probe over the measurement plane to generate the enhanced accuracy in planar near-field (NF) to far-field (FF) transformation than over the classical Fourierbased modal expansion methods. It is also illustrated that this method provides reliable results for cases when the conventional method fails, particularly, for the case, when the actual source plane and the measurement plane are approximately equal in size. Also, in this approach, there is no need to incorporate probe correction unlike in the existing approaches. In addition, a methodology can be designed where one can use an array of probes instead of moving a single probe over the measurement plane, thus improving the accuracy and efficiency of the measurements. In the use of the probe array, there is also no need to perform the probe correction. This proposed novel methodology is accomplished by solving for the equivalent magnetic current over a plane near the original source antenna under test, and then, employing the method-of-moments (MoM) approach to solve for the equivalent magnetic currents on this fictitious surface. For this proposedmethodology, even though, there is no need to satisfy the Nyquist sampling criteria in the measurement plane, a super resolution can be achieved in the solution of the equivalent magnetic current so that one can predict the status of the operation of each antenna elements in an array. Also, the presence of evanescent fields in the measurements does not make this methodology unstable unlike in the conventional Fourier-based techniques. The two components of the equivalent magnetic currents can be solved independently from the two measured components of the electric fields by solving the resultant MoM matrix equation very efficiently and accurately by using the iterative conjugate gradientmethod enhanced through the incorporation of the fast Fourier transform techniques. Sample numerical results are presented to illustrate the potential of a novel planar NF to FF transformation applied to the planar NF measurement technique. Index Terms-Antenna diagnostics, conjugate gradient method, equivalent currents, fast Fourier transform (FFT), integral equations, measurements without probe correction, planar near.