Рубрика: ACTIVE ANTENNAS

Radio Propagation in a Magnetized Plasma

Before proceeding with a discussion of the Appleton (mag — netoionic) equations, we need to define two quantities con­tained explicitly in the equations. The first is v, the number of collisions per second (collision frequency) between electrons and heavier particles (ions and neutrals). Another quantity, the gyromagnetic frequency or gyrofrequency, is the natural frequency (Hz) […]

The Virtual Height Concept

If we consider an RF pulse traveling vertically upward into the ionosphere at the speed of light, v = c, it will be reflected at the virtual height, h’. The time required for the pulse to be reflected from an ionospheric layer and return to the earth is space velocity c. Referring to the geometry […]

PHYSICAL PRINCIPLES AND MATHEMATICAL DESCRIPTION OF ELECTROMAGNETIC INTERACTION WITH THE IONOSPHERE

Because of the complexity of the terrestrial ionosphere (a weakly ionized plasma with a superimposed magnetic field in which electric currents flow), we must utilize the magne — toionic theory to quantify the ionosphere physical parameters. The most successful formulation of the appropriate magne- toionic theory was derived by Appleton and others in the mid […]

Extrahigh Frequencies

At EHF and above, propagation is primarily LOS, and be­cause of the higher frequencies (f a 300 MHz), these signals are less affected by the ionosphere than lower frequencies. On earth-space paths that traverse the equatorial and/or high — latitude ionosphere, however, the signal quality can be sig­nificantly degraded. These effects will be described below. […]

Very High Frequencies

Propagation in the VHF band (30 MHz to 300 MHz) is pri­marily by line of sight (LOS) to the optical horizon, so if the antenna patterns direct most of the RF power in the hori­zontal plane, there are essentially no ionospheric effects. For earth-space propagation paths, however, the ionosphere can affect the signal adversely by […]