Directional Antenna Polarization Demystified
A lot of our customers have questions when it comes to mounting antennas both inside and outside the building. The cell phone booster system works beautifully when the 3 components (amplifier, donor antenna, receiver antenna) all work in harmony. To understand this principle , lets talk about antenna polarization first. The polarization of an antenna always has an electrical component and magnetic component perpendicular to each other. The antennas are generally either omni-directional or uni- directional. Omni directional antennas receive and transmit signals in a 360 degree radiation pattern. What this means is that these type of antennas are suited for situations where the cell tower is going to change its position relative to the user. This is particularly the case of cell phone booster systems used in vehicles, where the user is moving in relation to the cell phone tower.
In the case of uni directional antenna, or the Yagi antenna is the antenna of our interest. The yagi antenna has elements arranged in a pyramid shape, it is easy to visualize the old TV antennas. The elements design dictates the spacing, 1/4 th or 1/10 th spacing between elements. The antenna consists of a drive element, reflector and and single directors. The driven element is the only part of the structure that is connected to the power source. The rest are feeding off of that driver and exactly 180 degrees out of phase with the driver and creates the polarization effect in directing the signal in a particular direction. The parasitic elements are less then or greater then λ/2, keep them out of phase with the director element. The director is the spine of the structure if it makes things easier to understand while the driver elements are the ribs sticking out of the spine.
The oscillation pattern above illustrates the oscillation of various elements of the yagi antenna. due to the careful design of the elements of the yagi, the transmission is directed in the forward direction then that of the backward direction. This direction sensitivity is what makes the yagi unique when it comes to transmitting signal in a particular direction like a laser beam!