Linear Polarization
The directions of the electric E and magnetic H fields in a spatially propagating electromagnetic wave lie in a plane perpendicular to the direction of wave travel.
The field directions follow the “right-hand screw rule”: when rotating from the E vector, positioned vertically (Z-axis), to the H vector, lying in the horizontal plane (Y-axis), the screw’s advancement coincides with the direction of wave propagation (along the X-axis).
In the figure, the electric field component remains in the vertical plane at all times. The spatial orientation of this component defines the property of waves called polarization. The wave shown in this example is called vertically polarized. Depending on the method of wave generation, polarization can be horizontal or inclined. If it remains unchanged during propagation, the polarization is referred to as linear.
When radio waves are reflected from objects or scattered by atmospheric anomalies, the polarization vector may change.
Circular (Elliptical) Polarization. RHCP, LHCP
When a radio wave propagates in free space, the tip of the electric field vector traces an ellipse in a plane perpendicular to the wave’s direction of travel — this is elliptical polarization.
Elliptical polarization is a combination of rotational and oscillatory motions, in which the electric field vector traces an ellipse. The ellipticity ratio is defined as the ratio of the lengths of the ellipse’s major and minor axes and is expressed in decibels. In extreme cases, with a zero minor axis, linear polarization results; with equal axes, circular (rotational) polarization occurs.
Circular polarization is classified as right-hand RHCP (right-hand circular polarization) and left-hand LHCP (left-hand circular polarization). Polarization is left-handed if the vector tip rotates clockwise when viewed toward the wave, and right-handed if it rotates counterclockwise.
Applications of Circular Polarization
Unlike linear polarization, radio waves with circular polarization do not change the polarization vector when passing through a scattering medium. Reflected parasitic signals instead reverse the rotation direction of polarization. Moreover, for receiving a circularly polarized signal, the relative orientation of transmitting and receiving antennas is not critical.
This property is used when receiver and transmitter antennas cannot be precisely aligned: in space communications, FPV systems, RFID tags and receivers. Circular polarization of light is also applied in stereoscopic cinema technologies such as RealD and MasterImage.