GPSGlobal Positioning System

GPS (originally Navstar GPS) is the world's first and most-used GNSS, operated by the US Space Force. The constellation maintains at least 24 satellites in six 55°-inclined orbital planes at roughly 20,200 km altitude — currently 31 active satellites in 2026, providing redundancy and global coverage.

GPS broadcasts civilian signals at L1 (1575.42 MHz, C/A and modernised L1C codes), L2 (1227.6 MHz, L2C since Block IIR-M), and L5 (1176.45 MHz, safety-of-life since Block IIF). The L1 C/A signal is the universal baseline that every GNSS receiver supports; L2C and L5 require modernised receivers and unlock dual- and triple-frequency precision modes.

Restricted military signals — P(Y) code on L1/L2 and modernised M-code on L1/L2 — provide hardened, encrypted PNT to US and allied military users. These are not relevant to civil receivers but matter for defense-grade antenna design (out-of-band rejection, anti-jamming margins).

Detailed signal specifications are defined in IS-GPS-200 (legacy), IS-GPS-705 (L5), and IS-GPS-800 (L1C). Any antenna marketed for GPS L1/L2/L5 must hold its phase center and gain across the centred 24 MHz wideband for L5 and across the ±10 MHz around L1/L2 for full code-and-carrier reception.