Short answer
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).
Detailed explanation
A choke-ring antenna surrounds the radiating patch (or dipole) with three or more concentric circular grooves, each roughly a quarter-wavelength deep at the design frequency. The grooves behave as short-circuited transmission lines that present infinite impedance at the open end — efficiently absorbing or scattering any energy arriving at low elevation (such as ground-bounce multipath).
The result is a sharp 3D radiation pattern with deep nulls at and below the horizon, near-zero response to LHCP (the polarisation reflected signals typically come back with), and an exceptionally stable phase centre across signal arrival angles. These three properties make choke-ring antennas the universal choice for geodetic CORS, fundamental reference stations, IGS network sites, and other permanent installations where measurement integrity is critical.
The 3D variant (introduced in the early 2000s by Leica / NovAtel / Trimble / Topcon, and offered by GNSource as the TDXL-CA341) extends groove geometry into the third dimension — depth-tapered rings that maintain the absorption property across the full multi-constellation L-band rather than just L1/L2.
Trade-offs: choke rings are heavy (5–10 kg), bulky (350–400 mm diameter), expensive ($1.5–5k retail), and have substantial wind loading. They're never used on moving platforms — only on permanent monuments. For mobile RTK or UAV applications, a multi-band helical or patch antenna is the right choice.
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.
Phase center
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.
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.
Patch antenna
A flat ceramic or PCB GNSS antenna with a single dielectric-loaded radiating element on a ground plane. The dominant antenna type for compact, low-cost, vehicle, and OEM applications — ranging from 18 × 18 mm pucks to 100 mm survey-grade discs.