Transient Fields of Parabolic Reflector Antennas

Abstract

Requirements to increase the information content of radar and communication systems result in a band width increase and are a reason to investigate and describe the transient fields from ultra wideband (UWB) large antennas¹. Furthermore, a need in such an analysis occurs in near field time domain antenna measurements². In these cases not only the transient far field is of interest. The spatial-temporal near-field distribution is useful too to the optimal antenna arrangement on the complex objects. Mention must be made that many issues of the theory of an impulse radiating antenna. (IRA) are discussed by Carl E. Baum. Everett G. Fart and D. V. Giri^3–8. The transient field from the circular focused aperture with uniform held distributions was considered in³. Much attention is given to IRA which consists of a large angle conical TEM feed that attach to a reflector antenna. It was shown that radiated held includes three distinct pacts. The first of these is the direct radiation from the feed structure (prepulse), whirl is of rather low magnitude, but lasts for a fairly long time This is followed by an impulse, which lasts for a brief time and is high in amplitude. Finally, there is a tail expected after the impulse. Closed-form expressions for prepulse were presented in ⁴. Analysis was extended to include the diffracted fields from the launcher plates and the circular rim of the reflector⁵. It was shown that there is an exact time-domain match of the spherical and planar TEM waves (inhomogeneous) at the reflector^4–7. Thu exact expressions for the acoustic fields on the z axis for a circular aperture were obtained in ⁸. While the above-mentioned works describe basic properties of transient fields of an IRA, many questions are yet to be investigated.