Geodetic reference networks require extremely precise antennas. Reference networks serve multiple roles, including the performance monitoring of all signals broadcast by each GNSS constellation and producing accurate and precise GNSS measurements. Reference networks, which are used to enable RTK and PPP applications, consist of reference stations that require antennas that have the tight phase centre variation and precisely known phase centre offset.
Geodetic quality antennas require a precise calibration, that estimates the phase centre offset at various frequencies (GPS L1, L2 and L5 are typical). In addition to the phase centre offset, the phase centre variation as a function of azimuth and elevation angle is also calibrated, enabling the observations to be adjusted correctly. Additionally, to minimize multi-path choke ring antennas may be a required option.