GNSS Engineering Reference
GNSS & antenna engineering glossary
Plain-language definitions for the terms that come up when working with GNSS receivers, antennas, and post-processing software. Each entry links to the GNSource product line where it shows up and the companion tool you can use to explore it interactively.
31 terms across 16 letters
ATerms starting with A
Anti-jamming
Techniques and equipment that maintain GNSS reception in the presence of deliberate or accidental RF interference. The main hardware approach is a CRPA (controlled reception pattern antenna); software approaches include narrow-band filtering, AGC compression detection, and pulse blanking.
Anti-spoofing
Detection and rejection of false GNSS signals — typically broadcast by an attacker who wants to misdirect a receiver to a false position or time. Distinct from anti-jamming; spoofing attacks use plausible-looking signals, not raw noise, so the receiver has to authenticate rather than just power through.
BTerms starting with B
CTerms starting with C
C/N₀Carrier-to-Noise Density Ratio
The ratio of received signal power to noise power spectral density at the receiver. Expressed in dB-Hz (because the ratio has units of Hz). A clean rooftop GPS L1 receiver should see 45–50 dB-Hz on strong satellites; below 25 dB-Hz the receiver loses track.
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).
CORSContinuously Operating Reference Station
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.
CRPAControlled Reception Pattern Antenna
An adaptive antenna array (typically 4, 7, 11, 16, or 32 elements) that electronically steers nulls toward jamming sources and / or steers beams toward GNSS satellites in real time. The standard anti-jamming hardware for military and high-value civilian GNSS receivers.
DTerms starting with D
ETerms starting with E
ECEFEarth-Centered Earth-Fixed
A 3-D Cartesian coordinate system with origin at Earth's centre of mass, X axis through the prime meridian / equator, Z axis along Earth's rotation axis. The native frame in which GNSS receivers compute satellite and user positions before projecting to lat/lon.
Ephemeris & Almanac
Two related types of orbital data broadcast by GNSS satellites. Ephemeris gives precise (cm-class) satellite positions, validity 4 hours. Almanac gives coarse (km-class) positions for the entire constellation, validity weeks. Receivers need both for cold start.
GTerms starting with G
Galileo
European GNSS, fully operational (FOC) since 2024. Civilian-controlled, with signals on E1 (1575.42 MHz, GPS-L1 interoperable), E5a/E5b (1176.45 / 1207.14 MHz), and E6 (1278.75 MHz, carries the free HAS PPP service).
GLONASSGlobalnaya Navigatsionnaya Sputnikovaya Sistema
Russian GNSS, operational since 1995 (re-established 2011 after a coverage gap). Uses FDMA channelisation on legacy L1OF (1602 MHz) and L2OF (1246 MHz) signals; modern CDMA signals (L1OC / L2OC / L3OC) align with the rest of GNSS.
GNSSGlobal Navigation Satellite System
Umbrella term for any constellation of satellites providing global positioning, navigation, and timing. The four global GNSS systems are GPS (US), GLONASS (Russia), Galileo (EU), and BeiDou (China); QZSS (Japan) and NavIC (India) are regional.
GPSGlobal Positioning System
United States DoD-operated GNSS, fully operational since 1995. Broadcasts civil signals on L1 (1575.42 MHz), L2 (1227.6 MHz), and L5 (1176.45 MHz), plus restricted military M-code on L1 and L2.
HTerms starting with H
LTerms starting with L
L-band
The 1–2 GHz radio frequency band used by virtually every GNSS civilian signal. Most public GNSS signals cluster around 1176 MHz (L5/E5a/B2a), 1227 MHz (L2), 1561–1602 MHz (L1/E1/B1/GLONASS L1), and 1268–1278 MHz (B3I/E6).
LNALow-Noise Amplifier
An amplifier with very low added noise (typical NF 1–2.5 dB at L-band) placed as close to the antenna element as possible. Sets the cascaded noise figure of the entire receiver chain and lets the antenna drive long cable runs without C/N₀ loss.
MTerms starting with M
MGRSMilitary Grid Reference System
A compact alphanumeric grid coordinate system built on top of UTM, used by NATO, US DoD, aviation, and search-and-rescue. A typical MGRS reference like 33TUM1234567890 encodes a position to 1 m precision in 15 characters — survives voice transmission and SMS reliably.
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.
NTerms starting with N
PTerms starting with P
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.
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.
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.
PPPPrecise Point Positioning
A precise GNSS positioning technique using globally-broadcast precise orbit, clock, and atmospheric corrections to deliver decimetre-to-centimetre accuracy with a single receiver — no local base station required. Convergence times of 10–60 minutes for cm-level; instant for decimetre via PPP-RTK.
RTerms starting with R
RDSSRadio Determination Satellite Service
BeiDou's unique two-way satellite messaging service. Users transmit a short message + position request on L-band uplink (1610–1626.5 MHz), and receive a response + correction on S-band downlink (2483.5–2500 MHz). The only GNSS with built-in global SMS-grade communication.
RINEXReceiver Independent Exchange
The standard text-based file format for storing raw GNSS observations (.YYo files), navigation messages (.YYn), and meteorological data (.YYm). All survey-grade receivers can write RINEX, and all post-processing software can read it. Versions 2.11 and 3.05 are the most common.
RTKReal-Time Kinematic
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.