Plane wave synthesis : a new approach to the problem of antenna near-field/far field transformation
In the recently evolved fields of satellite and space communications as well as in a number of related areas, a vital requirement is an accurate knowledge of the radiating and receiving characteristics of the transmitting and receiving antennas as they appear at a large distance (in the so called far-field region). It is often impossible to obtain a direct measurement of the performance of an antenna and in such cases where it is possible, the accuracy obtainable is frequently limited by the many difficulties associated with the process. Over recent years, a number of techniques have begun to appear which allow measurement of data close to the test antenna (in the near-field region) and then by mathematical processing (the transformation) predict what the far-field performance will be. The earlier techniques while being basically simple from a mathematical viewpoint, were not completely general and tended to involve special, sophisticated, hardware. The later techniques use the most general spherical scanning system but involve much more complicated processing. A new approach to the problem is presented in which much of the computational burden is pre-processed so that the size and complexity of the ultimate prediction task is reduced. The various measurement systems are considered briefly and the spherical system is formulated in detail. Simulated and experimental predictions are carried out and studies are included of the various errors likely to be present and their effects. The important parameters, including the sampling criterion, are discussed in some detail. It is shown that this technique has the potential for producing rapid and accurate predictions of antenna far-field patterns including the facility of compensation for the characteristics of the measurement probe.