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RTK High-Precision GNSS Antenna: Anti-Multipath and Phase Center Control

Quick Highlights

  • RTK high-precision positioning relies heavily on eliminating multipath interference and ensuring phase center stability.
  • Ground-station antennas commonly use choke-ring structures, while airborne UAV antennas require lightweight anti-multipath designs.
  • Multi-feed and multi-band antenna designs are used to control phase center variation and overlap across GNSS frequency bands.

To achieve centimeter-level or even millimeter-level accuracy, RTK (Real-Time Kinematic) relies heavily on eliminating multipath interference and ensuring phase center stability.

Article Contents

  1. I. Anti-Multipath Engineering Design
  2. II. Phase Center Control (PCO / PCV Correction)

I. Anti-Multipath Engineering Design

Multipath interference refers to the delay in phase ranging caused by satellite signals being reflected from buildings, the ground, or drones.

Choke Ring and 3D Choke Ring Structure

Principle: Ground station antennas commonly use concentric circular metal trenches (approximately λ/4 deep). When low-elevation-angle signals or reverse-polarized waves reflected from the ground are incident, high impedance is generated within the trench, preventing surface waves from entering the central antenna element.

Lightweight Improvements for UAVs: Airborne antennas cannot support heavy traditional chokes; therefore, a ceramic micro strip structure + EBG (Electromagnetic Bandgap) grounding substrate is used to block refracted waves through geometric microstructure.

Utilizing Circular Polarization Characteristics (RHCP Reversal Suppression)

GNSS direct waves are right-hand circularly polarized (RHCP), which reverses to left-hand circularly polarized (LHCP) after a single reflection. High-precision RTK antennas minimize cross-polarization gain, maintaining extremely high axial ratio purity (Axial Ratio <1.5 dB), enabling the antenna to have an ultra-high attenuation rate (>20 dB suppression) for LHCP signals, directly filtering reflected waves at the physical layer.

RTK high-precision GNSS antenna diagram showing RHCP reversal suppression, LHCP rejection, axial ratio, and cross-polar attenuation.

RTK GNSS anti-multipath and RHCP reversal-suppression diagram supplied with the approved article.

II. Phase Center Control (PCO / PCV Correction)

The "electrical phase center" of a GNSS antenna receiving signals is not a fixed physical point; it varies with the signal's incident angle (Elevation/Azimuth).

Phase Center Offset (PCO): The fixed three-dimensional distance between the physical geometric center and the average phase center.

Phase Center Variation (PCV): Dynamic fluctuations that occur with changes in satellite elevation angle.

Solutions
  1. Multi-feed Network: The antenna element uses 2 or 4 symmetrical feed points. Coherent combining technology ensures a highly symmetrical antenna pattern across the 360-degree azimuth, reducing PCV variation to within 1–2 mm.
  2. Tri-band/Multi-band Integrated Anti-interference Design: Integrating L1/L2/L5 (GPS/BDS/Galileo) ensures high overlap of phase centers across all frequency bands.

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