Intermediate and far fields of a reflector antenna energized by a hydrogen spark-gap switched pulser

Abstract

Previously, the design, fabrication and testing of a pulser with a parabolic reflector antenna, known as the prototype impulse-radiating antenna (IRA) has been presented. The paraboloidal reflector was fed by a TEM structure that in-turn was energized by a /spl plusmn/60 kV, /spl sim/100 atm. hydrogen switch operating in a burst mode at up to 200 Hz. The TEM structure also incorporated an electromagnetic lens to ensure a near-ideal spherical TEM wavelaunch. Some of the measured characteristics of this system were: (a) a peak electric field on boresight of 4.2 kV/m at a range r=305 m; (b) an uncorrected pulse rise-time (10-90%) of 99 ps; and (c) a boresight electric fields FWHM of 130 ps. The radiating system has now been more fully characterized with additional measurements and computations of near field, intermediate and far fields on the boresight. While the far fields from such a radiating system have been known for some time, the intermediate field analysis was only published recently. This method substitutes the radiated field from a paraboloidal reflector by the radiation field from the TEM structure reflected in the parabolic mirror. Although this work is limited to fields on the boresight at any distance from the antenna, the authors have been able to extend the analysis to the frequency domain. It has also been verified that the intermediate fields asymptotically tend to the far-field expressions, as the range r is increased. Good agreement between calculated and measured fields has been obtained for the prototype IRA in the near (r=5 m) and in the far field (r=305 m).