The linear movement of charges on a dipole antenna and monopole results in a linear polarization of the antenna. In case of a conventional micro strip patch antenna the charges move along the length of patch and produce linear polarization.
So on a circular polarized path there should be two direction of motion of charges for two polarization??
So is there a mathematical relation or theory related to it .i.e,
'vector movement of surface charges determine the polarization of antenna'?
Polarization is based on the plane from which the electric field component of the EM radiation is oscillating. If the polarization of the EM wave is offset rotationally from the polarization of an antenna, only a portion of the EM wave will be captured by the antenna. Hence, for optimum efficiency of a communication link, the polarization of the transmitting antenna and receiving antenna should be the same, if the antenna are referenced to the same plane. There are also other physical phenomenon that contribute to the choices of polarization for certain applications.
There are three main types of polarization, with many other possibilities. Typically, RF antenna are either linearly or circularly polarized. Linear polarized antenna are generally either vertically polarized or horizontally polarized, while circularly polarized antenna are either left-hand or right-hand circularly polarized. There is a third common type of polarization, which is a complex combination of both linear and circular polarization, known as elliptical polarization.
Depending on the angle between the polarization vectors of a linearly polarized antenna and an EM wave, the maximum polarization losses of a linearly polarized system are at 45 degrees of each other. At 45 degrees of polarization vector offset, the maximum polarization losses would be 0.5, or 3 dB. For a circularly, and elliptically, polarized system, the calculations are more complex, and the maximum polarization losses can be up to 30 dB. This is why polarization can be used to isolate signals and antenna systems that could interfere with each other. Though there is polarization loss, antennas that are polarized in a different fashion will receive signals from EM waves with different polarization. Hence, there is a limit to the amount of isolation polarization provides.
The polarization of an antenna is most often chosen based on the application requirements. Certain applications benefit from different polarization schemes. For example, vertically polarized antenna may perform better with land-mobile applications, as vertically polarized EM waves tend to travel across the curvature better than horizontally polarized EM waves. Horizontally polarized schemes may perform better when applications that rely on the ionosphere, typically with long distance communication. Lastly, circular polarization is often used in satellite communications, as the circular polarization tends to perform better in mitigating fading caused from shifts in satellite orientation.
hi, for determining polarization of an antenna the designer should consider the direction of E_field component variations. in linearly polarized antennas such as simple dipole the variation of E_field is linear which can be in X or Y direction correspond to horizontal or vertical polarization. if we add two perpendicular linear polarizations with 90 degree phase shift, circular pol. will be produced. in circular pol. the E_field component rotates.
Yes, for a circularly polarized antenna the direction of charge movement (current) rotates. The rotating current pattern is usually composed of two separable currents, each of which does not rotate, at 90 degrees angle to each other and a quarter of a wave period different in time - currents can be added linearly.
Mathematically, the circularly polarized current is the sum of the two complex vectors - the vectors give the direction in space, and the complex number gives the phase.
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