Evaluation of the Intermodulation Product Performance of Reflector Antennas and Related Structures by Microwave Imaging

This paper describes new developments that have been made in the adaptation of microwave imaging to locate sources of intermodulation product (IMP) generation upon microwave reflectors and related structures, and to predict the directions of IMP radiation. The objective of this study is two fold. Firstly to provide a means of evaluating the IMP performance of reflector antennas and, by locating the sources of IMP present, to show how it might be possible to improve the IMP performance by reducing or eliminating these sources; secondly, the imaging process enables the study of the causes and effects of IMP generation upon reflectors and similar structures. For conventional microwave imaging and antenna metrology, the object under investigation is illuminated at a single frequency and acts as a passive scatterer to this illumination. In the present case however, the object is illuminated by high-power source feeds at at least two different frequencies, inducing an active response in the form of IMP radiation. Where the structure constitutes a distributed source, the relationship of the IMP beams to the illumination may be determined.