G. Leone

Preliminary Results in Antenna Pattern Determination from Fresnel Field Amplitude Measurements

A pattern reconstruction algorithm from only amplitude field measurements is considered. Starting from two sets of Fresnel field data an iterative procedure enables to obtain an estimate of the corresponding phase functions. In this way the far field of the antenna under testing can be reconsctructed.

Far field transformation by only amplitude measurements: Cylindrical scanning

A suitable numerical processing is then applied for the far field reconstruction. Several transformation schemes have been developed for different geometries of the scanning surface, the choice among them being made according to the radiating properties of the antenna under test and to the required hardware complexity. In fact a trade-off between the mechanical specifications on the scanning system and the numerical processing complexity must be made. High accuracy in the reconstructed pattern requires high accuracy in the measured amplitude and phase of the near field. The achievement of such accuracy is much more difficult for the phase measurement than for the amplitude one. In fact the probe positioning errors of the scanning system result essentialy in uncertainities on the detected phase. Furthermore, the phase measurement is more sensitive than the amplitude one to the equipment inaccuracies. In this way tight requirements are to be imposed both on the mechanical and the electrical properties of the scanning system. These problems become critical especially in the millimeter wave range, because the displacement errors are of the same order of magnitude as the wavelenght. Therefore the availability of a transformation procedure based on only amplitude near field measurements is very appealing. Some early results for the spherical Fresnel zone scanning and planar near zone scgnning have been presented in [1,2]. In the following we will discuss some results obtained for the near zone cylindrical scanning. These results can be extended also to the near zone spherical

Antenna Far Field Reconstruction by a Minimum Near Field Measurements

The sampling approach for radiated fields has been proved effective in reducing to a minimum the number of information required for the field reconstruction in a prescribed angular range. Moreover the pseudo sampling series, which represents the fields both in the far and in the near zone, can be introduced. In this paper a pseudo sampling based near field-far field transformation technique is presented and its properties are shown. The influence on the reconstructed far field pattern of the probe positioning and the measurement errors is considered as well. In this way a relevant reduction in the number of measurements can be achieved with respect to the already existing techniques.