Circular Polarized Antennas
Circular Polarization is one of the biggest step forward in the progression of the FPV experience of the last few years. It has improved signal reception on all bands and brought 5.8Ghz video from one of the least practical systems to now one of the best.
What is Circular Polarization ?
Linear, meaning straight. The signal comes out between each end of the antenna normally in a vertical wave. If the antenna is positioned so its horizontal it comes out as a flat horizontal wave. This is vertically polarized and horizontally polarized.The diagram to the right shows a vertically orientated antenna, N being the top of the antenna S being the bottom. The waveform comes out from top to bottom in a linear fashion.
Circular polarization is emitted from the antenna in a circular spiral pattern.
Depending on the antennas polarization it can come out in a clockwise circular pattern, or a anticlockwise pattern. This we call right hand or left hand polarization. As you can see from the picture, if the antenna is positioned horizontal, vertical or any where in between the signal from it is exactly the same.
Whats the point ?
The circular pattern is the key to its success. With a linear antenna, for the best signal, or most information received by the receiver antenna, both antennas have to be of the same orientation. If they are everything is fine as long as you are in range. However, FPV having a moving antenna on the plane, this then means the antennas orientation will move depending on the planes position, its banking angle and its angle of attack.
With linear antennas, as soon as the transmitter antenna is away from the matching angle of the receiver antenna you incur losses in dbi. The further off axis the higher the dbi loss until the transmitter antenna is at 90 degrees off when you get the maximum -26dbi loss. During the dbi loss you can get from a drop in picture quality to total loss of picture.
With circular polarization however, no matter what axis the transmitters antenna is placed at, the circular pattern still matches the receiver so no losses are incurred at all. So your picture stays perfect all the time.