By Shung-Wu Lee (auth.), Y. T. Lo, S. W. Lee (eds.)
Techniques in keeping with the tactic of modal expansions, the Rayleigh-Stevenson growth in inverse powers of the wavelength, and likewise the tactic of moments answer of quintessential equations are primarily limited to the research of electromagnetic radiating constructions that are small by way of the wavelength. It as a result turns into essential to hire approximations in line with "high-frequency suggestions" for appearing a good research of electromagnetic radiating structures which are huge when it comes to the wavelength. the most flexible and helpful high-frequency thoughts is the geometrical concept of diffraction (GTD), which was once built round 1951 via J. B. Keller [1,2,3]. a category of diffracted rays are brought systematically within the GTD through a generalization of the options of classical geometrical optics (GO). in accordance with the GTD those diffracted rays exist as well as the standard incident, mirrored, and transmitted rays of cross. The diffracted rays within the GTD originate from convinced "localized" areas at the floor of a radiating constitution, reminiscent of at discontinuities within the geometrical and electric houses of a floor, and at issues of grazing occurrence on a soft convex floor as illustrated in Fig. 1. particularly, the diffracted rays can input into the move shadow in addition to the lit areas. therefore, the diffracted rays totally account for the fields within the shadow zone the place the move rays can't exist.
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Extra info for Antenna Handbook: Theory, Applications, and Design
With respect to state (k, u) we define a gain g(k, u) 4n l(k, u) = P 4n 1A(k)'u* 12 = =P n n pG(k) (64) = 4n intensity of the antenna in state (k, u) a reference power Again, depending on the reference power Pn , there are three gains gb g2, and d, which are analogous to the cases associated with (60). These three gains are illustrated in the upper half of Fig. 14. The gain defined in (64) is called the partial gain for a specific polarization u. The (total) gain G(k) in (60) is the sum of partial gains for any two orthogonal polarizations: G(k) = g(k, u) + g(k, v) which follows from (58).
In other words, dual sources and media imply dual fields. In some dual scattering problems the sources are not explicitly specified. We are given instead the incident field (El, H1) in problem 1 and field (E~, H~) in problem 2. Then, these two problems remain dual provided that (la) and (lb) are replaced by *The symbol A -> E;(r) ~ HHr) (3a) H;(r) ~ -E~(r) (3b) B means replacing A in problem I by B in problem 2. 2-5 2-6 Fundamentals and Mathematical Techniques B a I I (PMC)2 I I \ Y.? r---i I (E I • HI) I .........
In terms of (66) the gain definition in (60) has the following interpretation: G(k) J(k) (k) = J. ISO intensity of the antenna in direction k intensity of an isotropic radiator fed by the same power =~--~--~~~--~--~--~~--~---------- (67) We often express the dimensionless G by its decibel (dB) value: 1OloglOG. Sometimes we write dB as dBi, where the letter "i" emphasizes that the gain is over an isotropic radiator. Consider an antenna with gain G(k) fed by an input power Pn- Its radiation intensity J(k) would be the same as that for an isotropic radiator if the latter were fed with an input power given in watts by EIRP = PnG(k) (68) where EIRP stands for equivalent (effective) isotropically radiated power.
Antenna Handbook: Theory, Applications, and Design by Shung-Wu Lee (auth.), Y. T. Lo, S. W. Lee (eds.)