Short axial length broad-band horns

Abstract

Ever-increasing antenna frequency bandwidth requirements for countermeasures applications and electromagnetic compatibility measurements have provided the impetus for the development of a series of very broad-band horns. In addition to the broad bandwidth, a substantial reduction in axial length over that of earlier models has been achieved for the two designs discussed in this communication. The first horn described covers the frequency range from 1.0-12.0 GHz with the flared portion of the horn having an axial length of 6 in as compared with 12 in for an earlier model. Although horn antennas are not commonly considered for use at frequencies as low as 0.2 GHz, the short axial length design appeared to be an attractive approach in developing a very reasonably sized antenna operating in the 0.2-2.0 GHz range. The technique of fabricating the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</tex> plane walls in the form of a grid was used in both designs as a means of maintaining the required <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</tex> -plane half-power beamwidths. The grid for the 1.0-12.0 GHz horn is of printed circuit form while the grid elements of the lower frequency horn are made of aluminum tubing. Electrical characteristics of both designs are presented, as well as some additional data for recent advances which indicate that a further reduction in axial length or an increase in bandwidth can be achieved with only a moderate rise in VSWR in the lower portion of the frequency range.