A review of the major developments in our understanding of electric antennas in space plasmas

Salient ideas in the history of the science of dipoles as an important part of space radio science are reviewed. From the onset of the space age, the study of spontaneous radio emissions in geospace has required accurate measurements of wave electric fields. This review starts with the work done early in the space age on distributed dipole behavior in cold magnetoplasmas. Evidence of the effects of hot-plasma wave modes and of the response of space plasma excited by active antennas led to a broadening of the dipole theory, to include the generation and detection of electrostatic waves. The observations of plasma nonlinearities during the operation of active dipoles required further explanation. Indications of nonlinearity included spectra implying parametric processes and the RF-pumping of ambient ions and electrons, in the dipole near fields. The challenge today of understanding the inherent complexity of dipoles in magnetoplasmas may be met by recourse to particle-in-cell methods to predict classic antenna properties, such as current distribution, impedance, radiated field, and effective length.