GEOG 862
GPS and GNSS for Geospatial Professionals

The Antenna and The Right Hand Circular Polarized Signal

Diagram of a right hand circular polarized signal
Right Hand Circular Polarized Signal

The antenna, radio frequency (RF) section, filtering and intermediate frequency elements are in the front of a GPS receiver. The antenna collects the satellite’s signals and converts the incoming electromagnetic waves into electric currents sensible to the RF section of the receiver. Several antenna designs are possible in GPS, but the satellite’s signal has such a low power density, especially after propagating through the atmosphere, that antenna efficiency is critical. Therefore, GPS antennas must have high sensitivity, also known as high gain. They can be designed to collect only the L1 frequency, L1 and L2, or all signals, including L5. In all cases, they must be Right Hand Circular Polarized, (RHCP), as are the GPS signals broadcast from the satellites.

Polarized waves oscillate in more than one direction. The electrical field vectors of the GPS Signal have a constant magnitude, but their direction rotates so that the electrical field vector of the wave describes a helix in the direction of propagation. Said another way, circularly polarized waves are those where the angle of the electric vector rotates around an imaginary line traveling in the direction of the propagation of the wave. The rotation may be either to the right or left. The GPS signal is a Right-Hand Circularly Polarized (RHCP) wave. You can illustrate it this way. With your right hand, give the thumbs up signal. Now, instead of pointing your thumb up, point it in the direction that the GPS signal is propagating. Your curling fingers show you the direction of the rotation of the field.