Antennae for ultra-high frequencies. I. Wide-band antennae

A discussion of u.h.f. oscillations on spheres and ellipsoids, and a comparison of the mathematical theories of various authors. The three cases, free and forced vibrations, and oscillations due to an incident wave, are dealt with separately and their damping factors, Q, due to radiation losses, are evaluated for the various modes of E and H oscillations. Spheres are shown to have very large radiation losses, and act as wide-band aerials. Analogies with quantum mechanics are explained, and the relation between Abraham's analysis for thin ellipsoids, and that due to Brillouin and others for nearly spherical resonators is dealt with in detail. Resonance curves for driven and receiving ellipsoids are given; they differ from those of L-C circuits in that the radiation resistance varies with frequency. For all but thin ellipsoids, the current and voltage are out of phase at resonance: the phase and quadrature components are illustrated graphically for a range of wavelengths covering several modes of oscillation.