A receiver that maintains a position fix in a quiet lab can still fail when a nearby transmitter, intentional jammer, or platform noise raises the RF floor. This GNSS interference test plan template gives integrators a controlled way to measure that failure point, document recovery behavior, and verify whether an anti-jam antenna improves usable PNT performance.
The objective is not simply to prove that GNSS works. It is to establish how much interference the complete system can tolerate, on which bands, from which directions, and with what effect on position, velocity, timing, and reacquisition. Use the same plan for baseline antenna testing, multi-element anti-jam antenna evaluation, receiver comparison, and acceptance testing after installation.
Define the Test Objective Before Selecting Equipment
Start with an operational requirement, not a generic pass or fail statement. A UAS integrator may need continuous GPS L1/Galileo E1 navigation during a low-power in-band threat. A timing system may prioritize holdover transition and disciplined oscillator stability. A survey platform may accept short degradation but require fast RTK recovery after the interference stops.
State the mission condition and the metric that matters. Typical metrics are 3D position error, horizontal error, timing error, carrier-to-noise density ratio (C/N0), number of tracked satellites, loss-of-lock events, navigation solution availability, and time to reacquire. For controlled testing, define whether the system must maintain a valid solution or may enter a specified degraded mode.
A useful objective statement is: “Verify that the installed GNSS system maintains a valid multi-constellation navigation solution under a specified GPS L1 and Galileo E1 interference level, with no more than 10 seconds of recovery time after signal removal.” The exact threshold depends on the receiver, mission, threat model, and applicable compliance requirements.
GNSS Interference Test Plan Template
Use this record as the core test document. Fill in values before test execution so the operator does not make pass/fail decisions from memory.
| Test field | Required entry |
|---|---|
| Test ID and date | Unique identifier, operator, location |
| System under test | Receiver model, firmware, antenna model, cable length, filter/LNA details |
| Antenna configuration | Standard antenna or anti-jam antenna, element count, orientation, ground plane |
| Supported bands | Example: GPS L1/L2/L5, Galileo E1/E5, BeiDou B1/B3/B1C, GLONASS L1 |
| Test objective | Required PNT behavior and measurable pass criteria |
| GNSS source | Live sky, simulator, or simulator plus live-sky configuration |
| Interference source | CW, swept CW, narrowband, wideband, pulsed, chirp, or platform-generated noise |
| Frequency and bandwidth | Center frequency, sweep range, occupied bandwidth, modulation if applicable |
| Power at antenna | Calibrated level in dBm or dBW, including cable and coupling losses |
| Arrival direction | Azimuth and elevation relative to antenna boresight |
| Test steps | Start level, increment size, dwell time, test repetitions |
| Data captured | C/N0, satellites used, solution status, error metrics, receiver logs |
| Pass/fail result | Result against stated criteria, anomalies, corrective action |
Keep the test record tied to the installed configuration. Replacing a cable, changing an antenna mount, adding a radome, or moving an LNA can change gain, pattern behavior, and susceptibility. A result for a bench assembly is not automatically valid for the vehicle or enclosure where it will operate.
Establish a Calibrated Baseline
Run a no-interference baseline before introducing any RF threat. Allow enough time for the receiver to reach its normal tracking and navigation state. Record satellite geometry, constellation availability, C/N0 by satellite and band, position statistics, timing data where relevant, and any correction service status.
The baseline should represent the environment that the interference result will be compared against. For a live-sky test, document weather, antenna view of sky, nearby structures, and local RF activity. For a simulator test, document scenario coordinates, satellite power settings, motion profile, ionospheric assumptions, and injected error conditions.
Repeat the baseline after the interference sequence. If the two quiet-state results differ materially, investigate the environment or equipment before accepting the test. Interference results are only useful when the reference condition is stable.
Measure Power at the Correct Reference Plane
Generator output is not the interference level seen by the antenna or receiver. Account for every attenuator, coupler, cable, amplifier, splitter, and radiated-path loss. For conducted tests, establish the calibrated power at the receiver input or at the antenna-port reference plane. For radiated tests, characterize the field setup and use a repeatable antenna-to-antenna geometry.
This distinction matters most when comparing antenna configurations. An anti-jam antenna may reject energy based on direction, polarization, spatial processing, filtering, or a combination of these. A single generator setting does not prove equal exposure unless the test geometry is controlled.
Build the Threat Matrix Around Bands and Directions
Do not test only a single CW tone at GPS L1 and call the result anti-jam validation. That test can be useful, but it does not represent every interference mode the receiver may encounter. Build a threat matrix that matches the operating bands and expected RF environment.
At minimum, include in-band CW interference at each mission-critical band, offset tones near band edges, swept or chirped signals, and broadband or noise-like interference if the risk profile supports it. Test GPS L1, Galileo E1, BeiDou B1C, and GLONASS L1 separately where those signals are used in the navigation solution. If the receiver uses L2, L5, E5, B3, or other protected bands, add those cases rather than assuming L1 performance applies across the system.
For multi-element GNSS anti-jam antennas, direction is part of the test. Rotate the radiated interference source across defined azimuths and elevations. A practical matrix may include boresight, four cardinal azimuths at low elevation, and one or more elevated angles. The required resolution depends on the antenna pattern, platform masking, and likely threat direction.
Execute in Controlled Power Steps
Begin below the expected susceptibility level and increase interference in fixed increments. Small steps give better threshold data but extend test time. Larger steps are acceptable for screening, then refine around the observed failure point. Use a defined dwell period at each level so the receiver has time to show loss of lock, navigation degradation, or adaptation behavior.
For each step, record interference power, waveform, frequency, direction, C/N0 change, tracked satellites, navigation solution state, and error metrics. Continue until the system fails the stated criterion or reaches the maximum safe test level. Avoid driving active antenna inputs or receiver front ends beyond their rated limits.
After reaching the highest level, reduce or remove the interference and measure recovery. Record the time to regain tracking, navigation solution, correction lock, and required accuracy. A system that resists interference but takes several minutes to return to operational accuracy may not meet a mission requirement.
Compare the Complete Installed System
Test at least two configurations when evaluating mitigation: the reference antenna system and the anti-jam configuration. Keep the receiver, firmware, GNSS scenario, cable routing, and test geometry unchanged. If an antenna requires a different supply voltage, interface module, or ground plane, document those differences because they are part of the deployed solution.
Report improvement as a measurable delta, such as additional interference power tolerated before loss of navigation, reduced C/N0 degradation at a fixed interference level, or faster reacquisition after threat removal. Do not rely on a single headline number. A configuration may show strong protection from low-elevation interference and less improvement from overhead energy. That result can still be operationally valuable if it matches the platform threat geometry.
Capture Failures That Are Not Position Loss
Position output alone can hide a serious degradation. Watch for mode changes, loss of a constellation, reduced satellite count, increased dilution of precision, timing alarms, RTK float transitions, and abnormal receiver resets. For critical infrastructure timing or defense-adjacent applications, retain raw receiver logs and the test equipment settings with the result package.
Also document unintended interactions. High-gain active antennas, nearby radios, DC-DC converters, data links, and payload electronics can create self-interference. A radiated external-jammer test does not replace an installed platform EMC assessment.
Set Pass Criteria That Support Procurement and Integration
A useful acceptance result identifies the exact tested configuration and the conditions under which it passed. “Anti-jam verified” is too broad for procurement or deployment decisions. State the bands tested, waveform, calibrated power, arrival angles, solution criteria, and recovery requirement.
For custom platforms, the antenna is only one part of the RF chain. Element placement, clear sky view, cable loss, receiver dynamic range, filtering, and software configuration affect the final result. Anti-jam Antenna systems can be selected around required constellations, bands, size, weight, and installation constraints, but the installed test remains the final proof of performance.
Treat the completed template as a deployment control document, not paperwork. When the platform, antenna position, receiver firmware, or RF environment changes, rerun the affected cases and preserve the comparison data. That discipline turns interference testing into a repeatable engineering decision instead of a one-time demonstration.
