Polarization
It is the figure traced out in time by the instantaneous electric field vector associated with the radiation field produced by an antenna. Electromagnetic waves in free space travel in a direction that is perpendicular to the direction(s) of oscillation of the electric and magnetic fields. For example, if an RF wave is traveling in the z-direction, the electric field could be oscillating in either (or both) the x- and y-directions (referred to as the horizontal and vertical directions).
Examples: (1) RF waves can be separated into vertical-only and horizontal-only polarized waves, both of which are a type of linear polarization. (2) Satellite signals are often circularly polarized, having both vertical and horizontal components rotating around the z-direction of wave propagation.
Return Loss
The difference between the power input to and the power reflected from a discontinuity in a transmission circuit. This parameter is often expressed as the ratio in decibels of the power incident on the antenna terminal to the power reflected from the terminal at a particular frequency or band of frequencies.
Example: Antennas often are designed to have a return loss of -10dB or less, meaning that at least 90% of the electrical energy generated by the radio is actually transferred into electromagnetic wave energy.
Voltage Standing Wave Ratio (VSWR)
Is another way to measure return loss. It is a ratio of the maximum to minimum amplitude (or the voltage or current) of the corresponding field components appearing on a line that feeds an antenna.
Examples: Antennas are designed to have a VSWR of 2.0:1 or less, meaning that at least 90% of the electrical energy generated by the radio is actually transferred into electromagnetic wave energy. Return loss of -9.6 dB is equivalent to a 2.0:1 (VSWR).
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