A time domain (TD) solution for the analysis of multiple diffraction of spherical waves after an array of nonperfectly conducting wedges with different interior angles is presented. The proposed TD solution is based on the representation of the inverse Laplace transform of the corresponding frequency domain solution in closed form, as it is given by a hybrid of the uniform theory of diffraction (UTD)-physic optics (PO) solution. The new formulation, validated with the results from technical literature, does not need to incorporate the TD version of the higher-order diffraction coefficients and allows for the calculation of large number of wedges. It has the major advantage in terms of the mathematical complexity and computation efficiency when compared with other TD solutions.
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.
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