Effects of loss on the determination of antenna energy and Q

摘要

Expressions for the stored energy and Q factor of an antenna in terms of its radiated spherical modes and reflection coefficient have been extended to include the effects of loss. Three variations are given for excitation by matched, voltage, or current generators, and the importance of the proper phase reference for the radiated fields is emphasised. Two low-Q, self-resonant spherical antennas are used to illustrate the application of the energy formulae with and without loss. The results for these examples are validated by direct integration of the electric energy and by self-consistency of the radiation and dissipation terms. Approximation equations appropriate for processing experimental data are derived, and their predictions are compared with the actual Q's for the examples. Estimates of the lossless Q's are determined from the lossy data.