(A) new near field scanning technique for antenna radiation pattern analysis based on uniform geometrical theory of diffraction

Abstract

A new and efficient method is presented for computing far field antenna atterns from spherical near field antenna measurement data. The method utilizes a novel Uniform Geometrical Theory of Diffraction (UTD) based transformation of spherically scanned antenna tangential electric near field measured values to present to obtain the antenna far field patterns more efficiently. If the tangential near fields on the spherical surface S enclosing AUT completely are only of the electric type by assuming S is replaced by perfact electric conductor (PEC), the field external to S can then be expressed, via an appropriate equivalence theorem, directly as the field produced by an equivalent magnetic surface current source distribution on PEC sphere S (PECS). The equivalent magnetic surface current density on PECS is exactly related to the measured tangential electric field on the original surface S. The field external to the PECS due to an equivalent magnetic surface current distribution on the same PECS can thus be expressed as an integral of the dot product of an appropriate dyadic Green````s function. A highly accurate and relatively simple asymptotic high frequency UTD form of this special dyadic Green````s function is presented in essentially closed form. Numerical results of the presented method show good agreements with those of far field pattern obtained from direct computation for various antenna configurations over the whole observation range. The method introduced in this dissertation is simpler in analysis and faster in computing than the conventional spherical modal expansion method. In this method, it is postulated that the measurement probe is ideal one. Generally, the practical antenna as a probe is used in a near field measurement, then the size of the probe influences the near field measurement in two way. Initial error of the practical probe is that the measurement signal is a weighted average of the field over the probe aperture, rather than the fiel...