Effect of Antenna Size on Gain, Bandwidth, and Efficiencyl

A theore tical analysis is made of the effect of antenna s ize on parameters 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 broad-band antenna is approxima tely equal t o that of the uniformly illumina ted aper t ure. If higher gain is desired , the antenna mus t necessarily be a narrow-band device. In fact, th e input impedance becomes frequency sensitive so r apidly that, for large antennas, no significant increase in gain over tha t of the uniformly illuminated aper t ure is possible. Also, if t he antenn a is lossy, t he efficiency falls rapidly as the gain is increased over that of the uniformly illumina ted aperture.