Standard positioning GNSS receivers typically determine range from the code modulated onto GNSS signal carriers. User accuracy is commonly meter-class and depends on satellite geometry, atmospheric conditions, multipath, supported bands and constellations, and receiver implementation.
Real-Time Kinematic (RTK) positioning exploits the much shorter carrier wavelength by eliminating common error terms such as satellite clock errors, ephemeris errors, and atmospheric delay variations in real time. Removing these common error terms makes it possible to resolve the carrier-phase ambiguity, i.e. the total number of carrier cycles between the satellite and the receiver. Range calculation based on the carrier wavelength can then be used to achieve centimeter-level positioning accuracy.
A conventional GNSS CRPA suppresses interference by continuously changing complex weights across its antenna elements. Each calculated weight set changes the composite phase response presented at the RF output. Inconsistent phase variations across carrier-phase ambiguity solutions will result in loss of RTK fix, even when the CRPA is successfully suppressing the interference sources.
The HEDGE CRPA series combines adaptive spatial suppression with proprietary phase stabilization algorithms. The null-forming weights remain free to form and adapt nulls, while the phase stabilization network compensates for the carrier-phase disturbance introduced by array processing. The resulting stable phase at the RF output allows the RTK GNSS receiver to maintain centimeter-level accuracy even in severely contested interference environments.
1. System Overview
The proposed multi-band RTK-enabled GNSS CRPA architecture provides independent spatial interference mitigation across the L1, L2, and L5 GNSS frequency bands while maintaining compatibility with external multi-band RTK GNSS receivers. Independent band-specific CRPA processing is applied to the received signals, and the interference-mitigated RF outputs are combined into a unified multi-band signal for GNSS positioning.
RF and digital receive chains are designed to maintain low group-delay variation and high linearity, minimizing distortion of the received waveform during reception and spatial filtering.
Stabilization of the antenna phase response under interference is particularly important for receivers that exploit advanced GNSS processing techniques such as precise code and carrier-phase tracking, long coherent integration, and dual-frequency ionospheric correction. This combination of multi-constellation reception, spatial interference mitigation, and carrier-phase preservation enables the CRPA architecture to support modern centimeter-level, high-accuracy RTK positioning.
The architecture is available in two multi-band configurations:
HEDGE-8016-C200: 8+8 Multi-Band CRPA
L1 + L5 or L1 + L2
Optimized for high-order spatial nulling and dense interference environments.
- Up to 7 independent nulls
- GPS: L1C, L1C/A, L2C, L5
- Galileo: E1, E5a, E5b
- BeiDou: B1C, B1I, B2a, B2b
HEDGE-8016-S130: 8+4+4 Multi-Band CRPA
L1 + L2 + L5
Independent adaptive spatial processing across all three bands, including both wideband GNSS bands (L2 and L5).
- Up to 7 independent spatial nulls on L1
- Up to 3 independent nulls per band on L2 and L5
- GPS: L1C, L1C/A, L2C, L5
- Galileo: E1, E5a, E5b
- BeiDou: B1C, B1I, B2a, B2b
2. RTK Positioning Principles
RTK is a carrier-phase based relative positioning technique that uses simultaneous GNSS observations from a reference station and a rover to achieve centimeter-level positioning accuracy.
The fundamental advantage of RTK comes from the high precision of the GNSS carrier-phase observable. Within the GNSS receiver, the incoming satellite carrier is tracked by a carrier-tracking loop, typically implemented as a Costas-loop PLL. The tracking loop continuously estimates the phase of the received carrier relative to the receiver’s local oscillator and produces a precise carrier-phase measurement.
An important distinction is that the PLL does not directly determine the integer ambiguity. The carrier-tracking loop provides an extremely precise estimate of the received carrier phase, including the fractional phase component. However, the absolute number of full carrier cycles between the satellite and the receiver is unknown.
RTK resolves this uncertainty by using simultaneous carrier-phase observations from both the rover and the reference station. The observations are differenced between the rover and reference receivers to eliminate or significantly reduce common sources of error.
An integer ambiguity-resolution algorithm then estimates and validates the most probable integer ambiguity set. Once the ambiguities are successfully resolved, the navigation solution transitions to the RTK-FIXED state, enabling centimeter-level relative positioning.
Maintaining the RTK solution depends on the continuity and consistency of the carrier-phase measurements used for ambiguity resolution. This requirement is particularly important in CRPA-based GNSS systems, where multiple antenna and RF channels are coherently combined before the signal reaches the GNSS receiver.
3. Carrier-Phase Integrity in GNSS CRPA Systems
Carrier-phase integrity is a critical consideration when CRPA-based interference mitigation is used in conjunction with RTK positioning.
A conventional CRPA architecture processes the received signals through multiple antenna elements, independent RF channels, and adaptive spatial-processing stages before presenting a combined signal to the GNSS receiver.
In conventional CRPA implementations, uncompensated inter-channel phase offsets and time-varying phase responses introduced by adaptive beamforming alter the effective carrier phase of the combined GNSS signal. Although these variations have limited impact on conventional code-based positioning, controlling them is crucial for RTK, where centimeter-level positioning depends directly on stable carrier-phase observations and reliable integer ambiguity resolution.
If the effective CRPA phase response varies over time, the resulting phase changes may appear as additional biases in the carrier-phase measurements observed by the GNSS receiver. This can increase carrier-phase residuals, degrade ambiguity estimation, and reduce the continuity or robustness of the RTK solution, particularly when the interference environment causes frequent adaptation of the CRPA weights.
The HEDGE architecture addresses this limitation with a proprietary phase stabilization algorithm implemented within the null-forming processing core. By preserving the carrier-phase integrity required by downstream RTK processing while simultaneously providing anti-jam protection, the architecture enables the GNSS receiver to maintain carrier-phase tracking and supports centimeter-level RTK positioning in interference environments.
4. Interference Test Setup and Conditions
The test setup is designed to evaluate the positioning performance of the HEDGE-8016 under multi-directional, spatially distributed interference conditions, while keeping the receiver and CRPA configuration fixed. In the simulated interference environment, seven transmit antennas were distributed around the HEDGE-8016 at approximately 51° angular spacing and a distance of approximately 3 m.
During the experiments, the average received interference power at the Device Under Test (DUT) was maintained approximately between −32 and −58 dBm, covering a range of significant interference conditions. As illustrated in Table 1, received interference levels in this range are representative of the levels that may occur at the DUT depending on jammer distance and radiated power.
| Distance to Jammer (m) | Received Interference Level at DUT (dBm) | Equivalent J/S (dB) |
|---|---|---|
| 30 | ≈ −20 | 110 |
| 110 | ≈ −30 | 100 |
| 340 | ≈ −40 | 90 |
| 1000 | ≈ −50 | 80 |
| 2500 | ≈ −60 | 70 |
The evaluation further includes a band-dominant interference condition in which the L1 signal is strongly suppressed. This edge-case scenario demonstrates the benefit of multi-band reception, as the L5 band remains available to support continued positioning despite severe L1-band interference.
5. Multi-Band GNSS RTK Positioning Performance
The RTK positioning performance of the HEDGE-8016 was evaluated under interference-free and spatially distributed interference conditions to assess its multi-band GNSS robustness.
Under interference-free conditions, the HEDGE-8016 demonstrated stable RTK-FIXED operation with centimeter-level accuracy:
- Fix mode: RTK-FIXED
- 2D positioning accuracy: 1 cm
- 3D positioning accuracy: 2 cm
- Average C/N0 across all bands: 37.3 dB-Hz
The system was subsequently evaluated under severe dual-band L1/L5 interference, where the resulting performance was measured at:
- Fix mode: RTK-FIXED
- 2D positioning accuracy: 3 cm
- 3D positioning accuracy: 5 cm
- Average C/N0 across all bands: 23.9 dB-Hz
Despite the challenging RF environment, the HEDGE-8016 maintained an RTK-FIXED solution with centimeter-level accuracy. Multi-band GNSS measurements enabled reliable high-precision positioning under interference, demonstrating the resilience of the HEDGE-8016 and the effectiveness of its multi-band CRPA architecture. Further details are available in the HEDGE Multi-Band CRPA Solution White Paper.
6. Conclusion
RTK positioning delivers centimeter-level accuracy (1–2 cm) in real time, compared to the meter-level accuracy of standard GNSS positioning. That precision creates a strict requirement: the antenna and GNSS receiver front end must not introduce unmodeled phase changes as the interference environment evolves.
Although conventional GNSS CRPAs can suppress spatially distributed interference, continuously varying complex weights and inter-channel phase biases can alter the composite phase response and effective phase center of the antenna, potentially preventing reliable RTK resolution.
The HEDGE CRPA architecture allows its adaptive weights to form and reposition interference nulls without compromising carrier-phase integrity. A proprietary phase stabilization network compensates for phase disturbances caused by null-forming array processing.
Experimental results demonstrate that the architecture can maintain high-accuracy navigation performance under severe multi-source interference. The HEDGE CRPA architecture therefore preserves centimeter-level RTK positioning in interference environments where conventional CRPA architectures experience loss of RTK resolution.
