Ctia-商务和通用航空RA实验室测试报告（英）-2023-21页_1mb

CTIA Radio Altimeter Coexistence with 5G: Lab Test Summary

Executive Summary

The report assesses radio altimeter (RA) coexistence with nearby 5G spectrum services in the 3400-4940 MHz range. As 5G expands into mid-band spectrum adjacent to the RA band (4200-4400 MHz), spectrum regulators and industries worldwide are addressing potential interference. CTIA conducted laboratory tests on BA/GA RAs, finding that custom bandpass filters significantly improved RA performance by rejecting out-of-band signals. Transmitter power also played a role in resilience. The next generation of RAs should incorporate better filters, higher power levels (near 30 dBm), and robust receiver designs to handle future spectrum reallocations.

Introduction

The exponential growth of 5G requires reallocating mid-band spectrum, often near aviation RAs, leading to coexistence challenges. DO-399 and new Minimum Operational Performance Standards (MOPS) are being developed to address this. CTIA commissioned tests to evaluate RA performance with 5G interference, emphasizing the need for industry cooperation to ensure safety in evolving spectrum landscapes.

Radio Altimeter Specifications

Current RA models vary in bandwidth, transmit power, and antenna design. Key models flown include those from FreeFlight, Garmin, Thales, and Honeywell. For instance, models like the FreeFlight RA-5500/6500 increased transmitter power by 6.4 dB, improving performance. Specifications highlight that some RAs tolerate strong adjacent signals, but others are less robust, pointing to design differences as critical factors.

Bandpass Filter Design

Custom filters were designed to narrow the passband and reject energy outside the RA band. Filters like MFC 20926 achieved a smaller form factor while providing strong out-of-band rejection. These filters, used in tests, demonstrated that optimized specifications can reduce size and weight, enhancing RA resilience without modifying core hardware.

CTIA Radio Altimeter Lab Test Setup

The tests replicated real-world conditions by applying C-Band 5G fundamental and spurious emissions. A transmitter leakage of 75 dB was used, following stricter criteria than prior AVSI tests. Key parameters included test heights (200, 1000, 2000 feet), loop losses (up to 97 dB), and RF inputs verified via spectrum analyzers and vector signal generators. The setup evaluated how RAs handle persistent, high-power interference.

Fundamental Emissions Test Results

With external bandpass filters, all RAs showed improved tolerance, reducing sensitivity to out-of-band signals like those at 4130 MHz and 4480 MHz. For example, RA models India, Alpha, Zulu, and Victor saw performance enhancements from -38 dB to +42 dB improvement across heights. Without filters, some models exhibited significant degradation.

Spurious Emissions Test Results

Spurious emissions tests revealed that some RAs, like India, needed redesign, while others performed well, with rejection levels improving resistances. The tests used Additive White Gaussian Noise (AWGN) in the RA band, identifying thresholds for acceptable interference levels.

Conclusions

The testing confirmed that custom bandpass filters and higher transmitter power levels can future-proof RAs against adjacent spectrum services. While some models perform well natively, all benefited from filter enhancements. Recommendations include industry-wide adoption of minimum 30 dBm transmit power, improved antenna designs, and continued research to align with new RA MOPS standards.