Protecting GNSS (the EPM side, Electronic Protective Measures, applied to navigation) works in layers. No single measure is enough on its own; together they raise the J/S threshold and close the spoofing back doors. The antenna is the first and often the most powerful line of defence — hence the distinction between FRPA and CRPA.
FRPA — Fixed Reception Pattern Antenna
A FRPA (Fixed Reception Pattern Antenna) is the ordinary GNSS antenna: a single element with a fixed, roughly hemispherical reception pattern that looks upwards to see all the satellites. It is the small "patch" or mushroom you see on practically every vehicle, aircraft and device.
- Advantages: small, light, cheap, no processing needed.
- Protection: limited. The pattern itself suppresses a little from the horizon and from below (where many jammers and multipath come from). A choke ring or reduced sensitivity at low elevation helps against ground-based interference and reflections, but the pattern is fixed: it cannot adapt to a jammer.
The FRPA is fine for civil and low-threat use, but it offers little against targeted jamming. For that you need an antenna that actively adapts: the CRPA.
CRPA — Controlled Reception Pattern Antenna
A CRPA (Controlled Reception Pattern Antenna) is an array of several antenna elements (typically 4 to 7) with an adaptive processor behind it. By combining the signals of the elements in phase and amplitude, the CRPA can shape its reception pattern in real time — exactly the same principle as adaptive null steering in radar antennas (Main lobes, side lobes and back lobes). Two methods, often combined:
- Null steering: the processor detects the direction(s) the jamming comes from and steers deep nulls in the pattern towards them — the signal from that direction is suppressed by tens of dB. An array with N elements can "null out" up to N−1 jammers at once.
- Beam steering: the processor points beams (extra gain) at the known positions of the satellites, which raises S.
- Advantages: very effective (jamming suppression of tens of dB), works against several jammers, and the directional sensitivity also helps against spoofing (Spoofing and meaconing) — signals that do not arrive from above, from satellite directions, are filtered out.
- Disadvantages: larger and heavier (an array of elements), more expensive, more complex processing, and strictly export-controlled. That is why a CRPA is fitted to combat aircraft, ships and precision weapons, and a FRPA to everything else.
FRPA = fixed pattern (one element, cannot adapt). CRPA = controlled pattern (several elements + processor, steers nulls towards jammers and beams towards satellites). The CRPA is the direct navigation application of the phased-array null steering from Main lobes, side lobes and back lobes.
Ukrainian sources (Militarnyi, Aug. 2026) report that the Gerbera and Geran seeker variants now carry a 12-element Kometa-M antenna — in principle a CRPA — combined with a system for automatic target detection and tracking that lets the drone steer itself to the target even after losing the operator link. If this is correct, it undermines the assumption that losing the C2/GNSS link stops a drone or forces it to "return to home" (see The two links to attack/17.4) — terminal guidance then becomes independent of the link. Source: Militarnyi, via a Ukrainian volunteer — not yet independently confirmed, but quoted by EW analyst Serhii "Flash" Beskrestnov.
Other protective measures
The antenna is the first layer; around it lies a whole package, just like the layered self-protection package against missiles (Electronic Counter Measures):
- More robust codes: M code and (classically) SAASM/P(Y) offer higher processing gain and cryptographic authenticity — the best structural protection against both jamming and spoofing (Codes and signals).
- INS coupling: an Inertial Navigation System (Inertial navigation) navigates entirely on its own using gyroscopes and accelerometers. Coupled to GNSS, the system can keep going during jamming ("coasting"), and it helps the receiver make its tracking loops narrower and therefore more jam-resistant. The combined GNSS/INS solution is the backbone of practically every modern weapon and platform.
- Multi-constellation & multi-frequency: using GPS, Galileo, GLONASS and BeiDou on L1/L2/L5 at the same time. An attacker then has to jam many more bands at once.
- Filtering & detection: filtering out narrowband and pulsed jamming, and detecting spoofing through power, time and plausibility checks and signal authentication (OSNMA).
- Alternative PNT: fallback sources such as eLORAN, celestial navigation, visual/terrain navigation and accurate clocks, so that losing GNSS is not fatal.
A concrete example of "alternative PNT" in practice: Ukraine's Maiachnia system (Skyline platform) is a chain of autonomous radio beacons along the Black Sea coast, from Ochakiv to Izmail. Interceptor drones (including the Wovkulaka Spitfire and the Techno Taras system) navigate by triangulating on these beacons and can thus return and find targets despite heavy Russian GPS jamming over the Black Sea. Reported results: record interceptions of Russian Orlan reconnaissance drones at 110 km and 86 km from the coast. Sources: Euromaidan Press / Militarnyi, Aug. 2026 — RU Mil Tracker.
The lesson is the same as everywhere in this discipline: no single measure stands alone. A CRPA buys suppression, M code buys resilience and authenticity, INS buys time, and multi-constellation buys breadth. Together they push the burn-through boundary (Overpowering the jamming signal) inwards and close the spoofing door.