Compact Aperture Antennas
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From an antenna perspective, arguably those that can be classed as ‘compact’ reside largely in the ‘aperture antenna’ camp. Consequently, this chapter endeavours to provide the reader with a fundamental appreciation of the radiation characteristics of aperture antennas by deriving the key integral equation for the auxiliary vector potential Am, which is analogous to the magnetic vector potential A. As in Chap. 2, Am is developed from the Maxwell equations. Once a knowledge of Am has been secured, the radiation properties of some regularly shaped apertures can then be examined. This leads to the derivation of spectrum functions which relate the far radiation field of the antenna, to the aperture field, through a Fourier transform pair. The relationships which exist between antenna directivity, gain, radiation efficiency and sidelobes, and how these basic properties are influenced by the aperture field distribution of the given antenna, is studied in detail, for both two dimensional and three dimensional radiation pattern examples. While this area of study has traditionally been associated with large antennas, here we show that the analytical techniques explored are equally applicable to compact antenna forms.