Effect of antenna size on gain, bandwidth, and efficiency

A theore tical ana lysis is m a d e of the effect of antenna s ize on para meters such as gain, bandwidth, and efficiency .Both near-zone and far-zon e direct ive gains are considered .It is found that t he maximum gain obtainable from a broa d-band a ntenna is approxima tely equal t o that of the uniformly illumina ted ap er t ure.If higher gain is desired , the antenna mus t necessarily be a narrow-band d evice.In fa ct, th e input impedance becomes frequency sensitive so r apidly that, for large a nte nnas, no significan t increase in gain over tha t of the uniformly illuminated aper t ure is possible.Also, if t he a ntenn a is loss y, t he efficiency falls rapidly as the gain is increased over that of the uniformly illumin a t ed aperture.