n-Band Scattering from Arrays with Parallel Feed Networks

Approximate closed-form expressions are derived for in-band scattering from an array antenna with parallel (corpo- rate) feed networks. Multiple reflections are neglected and feed devices of the same type are assumed to have identical electrical characteristics. The model is shown to be in good agreement with results generated using a scattering matrix formulation. Based on computed data, the characteristics of array scattering are discussed. I. INTRODUCTION CATTERING from antennas has been the subject of study since the 1950'~~ Dicke investigated the properties of antenna scattering with the intent of determining the antenna parameters (l). Extensive work has been done with regard to dipole scattering and the effect of the terminal-load impedance (2), (3). The radar cross section (RCS) of horns (4), (SI, reflector antennas (5), (6), microstrip patches (7), (SI, and arrays (9), (lo) have also been studied. In most of these works the antenna feed terminals are connected to lumped loads, and only (9) addresses the impact of the feed network on the antenna-scattering pattern. In this paper, scattering from arrays of elements with parallel (corporate) feed networks is examined. The frequency of the illuminating wave is assumed to be the same as the operating frequency of the array. Therefore, most of the received energy will be delivered to the load at the array terminals if the feed is well designed. However, even for well-matched arrays, small mismatches exist within the feed. For a large array these can number in the thousands. Reflected signals generated at each of the mismatches will return to the aperture and reradiate a scattered field. The total scattered power is a small percentage of the incident power, but the many mismatches can add coherently under some conditions, yielding a significant RCS.