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Electromagnetic whistler‐mode radiation from a dipole in the ionosphere

Dipole‐antenna radiation theory has been tested for electromagnetic whistler‐mode waves in the frequency range 0.1–1.3 MHz using data from the two‐point rocket experiment Observations of Electric‐field Distributions in the Ionospheric Plasma; a Unique Strategy (OEDIPUS) C. Waves were emitted from a double‐V dipole on a transmitting subpayload and received at a distance of about 1200 m on a similar dipole connected to a synchronized receiver. The magnitudes of transmitted signals predicted by a theory for short dipoles have been found to be in good agreement with observations. The agreement is very good in the top two thirds of the frequency range where the dispersion relation and the geometry provide only one saddle‐point solution with the required group direction. In this part of the parameter space studied, the transmitter‐receiver separation is at least 10 wavelengths. This is not always true at the lowest frequencies, where the expected effects of interference of multiple saddle‐point rays and of the oblique resonance cone are observed.