Polarization and Cross-Polarization Level of antenna

The polarization of an antenna is the polarization of the electric field of the radiated
wave. Antennas can be classified as linearly polarized (LP) or circularly polarized
(CP). The polarization of the wave is described by the tip of the E-field vector as
time progresses. If the locus is a straight line, the wave is linearly polarized. If the
locus is a circle, the wave is circularly polarized. Ideally, linear polarization means
that the electric field is in only one direction, but this is seldom the case. For linear
polarization, the cross-polarization level (CPL) determines the amount of polarization
impurity. As an example, for a vertically polarized antenna, the CPL is due to
the E-field existing in the horizontal direction. Normally, CPL is a measure of
decibels below the copolarization level.