an overall length of about six inches 152 4 mm and has a diameter at its forward end 404 a of about three inches 76 2 mm a more traditional feed horn such as feed horn 304 in fig7 has a diameter of about 3 u2013 5 inches 76 2 mm u2013 127 mm at its forward end and an overall length of about three inches the hole 408 in the main reflector is preferably made slightly larger than what might be actually needed to permit a degree of longitudinal adjustment of the feed horn 404 relative to subreflector 412 the use of an elongated feed horn with a narrower forward end produces a more focused near field illumination of the subreflector 412 in practice the overall length of the feed horn 404 will typically be between 20 u2013 100 greater than the length of a standard wide angle feed horn such as feed horn 304 referring to fig9 arrow 416 represents the overall depth of the antenna 400 the depth 416 is significantly less than the depth indicated by arrow 320 in fig8 and substantially the same as the depth indicated by arrow 316 in fig7 thus the overall swept volume of the antenna 400 will be less than that produced by the antenna of fig8 and substantially the same as that produced by antenna 300 in fig7 the use of the hole 408 in the main reflector 402 thus.