Study of the oscillations stimulated at the upper hybrid resonance by a pulsed dipole antenna in a weakly inhomogeneous plasma

The oscillations, excited by a pulsed dipole antenna at the upper hybrid resonance in a weakly inhomogeneous plasma, are investigated by the Wentzel—Kramers—Brillouin (WKB) approximation. In addition to a direct component, the field at a given distance from the transmitter is shown to consist in two obliquely reflected rays when the upper hybrid frequency W T is less than twice the electron gyro-frequency W H . The analytical expressions of the frequencies of the echoes intercepted by a moving receiver are given and the influence of the reception time t , the velocity V S of the receiver and the parameters of the plasma are thus pointed out. As distinct from previous studies, the static magnetic field B 0 , the velocity of the receiver, and the gradient of the electron density ∂N/∂X, are here vectors of arbitrary directions. The choice of such a general model makes it possible to interpret most of the experimental data concerning the upper hybrid resonance in the ionosphere.