Determination of antenna far-field radiation-patterns from near-field data

Abstract

AsSsssssa In tlıis thesis a new method, based upon integral equation solution is developed for the prediction of far-field radiation patterns of optically large antennas from near-field measurements» A general formula of transmission between two antennas is derived using the concept of angular spectrum of plane waves and Brown6 s generalized reciprocity theorem. It is shown that, in the application of the well known Fourier transform method of radiation-pattern determination, the error produced by neglecting the directivity of the measuring probe oaa be corrected by a simple and rigorous method described in this thesis. The technique of antenna synthesis is presented and an integral equation is obtained whose solution yields the far- field radiation-pattern. It is shown that, if the near-field measurements are performed employing the antenna synthesis technique, then the spatial filtering action of the synthesized pattern reduces the computational work needed in pattern prediction considerably. She phase factor in the integrand also contributes to the filtering action of the synthesized pattern» The solution to the integral equation is obtained by expanding the unknown angular spectrum function into an orthogonal series making use of the sampling theorem. Thus, the problem of solving the integral equation is converted into the problem of simultaneous solution of a set of linear algebraic equations. t iii -For the detailed numerical study of errors in the solution of integral equation, a digital computer (IBS 360) is utilised. She theory presented in this thesis is -tested experi mentally by predicting various H-plane far-field radiation- patterns. The experimental results reveal a very good agreement between the direct-measured and predicted far-field patterns* IV