Short answer
The apparent electrical centre of an antenna — the point from which signal range is effectively measured by a GNSS receiver. Phase-centre stability (the variation in this point as the signal arrival angle changes) is the single most important parameter for survey-grade and geodetic antennas.
Detailed explanation
A real antenna is a 3-D structure (patch, helix, choke ring + radome) but a GNSS receiver treats the antenna as a single point — the phase centre — for range calculation. The phase centre is the point in space at which the antenna's electromagnetic phase response originates: if you shift the geometric mount point of the antenna by a few mm, the phase centre may shift by a similar (or different!) amount depending on signal arrival direction.
Two specifications matter. Phase Centre Offset (PCO) is the displacement of the average phase centre from the antenna's geometric reference point — a constant 3-vector, usually a few mm to a few cm. Phase Centre Variation (PCV) is the additional shift that depends on signal arrival angle (elevation and azimuth) — typically <1 mm for a well-designed survey antenna, <0.5 mm for a high-end choke ring.
The IGS and NGS publish antenna calibration files (igsXX.atx format) characterising PCO + PCV for each calibrated antenna model on each frequency. Any survey-grade processing software loads these files and applies the corrections per measurement — that's why "calibrated" antennas are required for IGS / EUREF / SOPAC submissions.
GNSource's measurement-grade products (CA341 choke ring, HA-series helices) are designed and characterised against IGS-class stability targets: the CA341 holds phase centre within ±1 mm across full multi-constellation L-band coverage and across signal arrival angles from 5° elevation to zenith.
Where you'll see this
High-Precision GNSS Measurement
Browse product lineRelated terms
Multipath
Distortion of a GNSS signal caused by reflections off nearby surfaces (buildings, ground, vehicles) arriving at the antenna nanoseconds after the direct path. Adds pseudorange noise of several metres in unmitigated urban environments — the dominant error source for many high-precision applications.
Choke ring antenna
A geodetic GNSS antenna with concentric corrugated grooves around the radiating element that absorb low-elevation signal reflections. Provides the best multipath rejection and most stable phase centre of any commercial GNSS antenna, at the cost of bulk and weight (typical 380 mm diameter, 5–10 kg).
Polarization (RHCP / LHCP)
The rotation direction of the electric-field vector in a GNSS signal. All GNSS satellites broadcast right-hand circularly polarised (RHCP) signals. Ground reflections flip handedness to LHCP, so an antenna that rejects LHCP automatically rejects single-bounce multipath.
RTK
A differential GNSS technique using carrier-phase measurements from a known base station to give a moving rover centimetre-level (typically 1–3 cm) horizontal accuracy in real time. The dominant high-precision GNSS technique for cadastral surveying, machine control, and precision agriculture.
CORS
A permanently-installed GNSS receiver streaming raw measurements 24/7. CORS networks are the backbone of RTK and network-RTK services, geodetic monitoring, and post-processed precise positioning. Typical inter-station spacing is 50–100 km for regional RTK, 200–300 km for national geodetic networks.