Frank H. Sanders, Geoffrey A. Sanders, Brian D. Nelson, and Robert L. Sole

Abstract:

The introduction of Fifth Generation New Radio (5G NR) base station transmitters into 2590–2690 MHz in the U.S., adjacent to the spectrum band 2700–2900 MHz used by air traffic control radars, has resulted in interference effects in some safety-of-life Airport Surveillance Radar Model 9 (ASR 9) receivers. This report describes work performed by the National Telecommunications and Information Administration (NTIA); the Federal Aviation Administration (FAA); the wireless carrier T-Mobile; and two 5G equipment manufacturers to understand and resolve this coexistence challenge. Although the problem initially appeared to be due to 5G unwanted emissions within the radar band, detailed work shows that this is not the case. Instead, a novel spectrum-spreading effect within the radar receivers generates power from adjacent-band 5G input signals on the receivers’ tuned, radar-band frequencies. This occurs despite the receivers being equipped with robust radiofrequency (RF) bandpass filtering. The effect is generated by solid-state RF switches in the receivers. The spectrum spreading is due to ordinary physics of the switches’ time-chopping of adjacent-band input 5G waveforms. Possible solutions are presented. This report is written as an illustrative case study, emphasizing not only the technical problem but also the study’s underlying scientific and engineering process.

Keywords: electromagnetic compatibility (EMC); air traffic control (ATC) radar; airport surveillance radar (ASR); 5G; 5G radiation; 5G NR; 5G emissions; 5G emission spectrum; 5G spectrum bands; electromagnetic coexistence; national air space safety; radar receiver interference; radio spectrum coexistence; radio spectrum compatibility; wireless coexistence with radars

Disclaimer: Certain commercial equipment, components, and software may be identified in this report to specify adequately the technical aspects of the reported results. In no case does such identification imply recommendation or endorsement by the National Telecommunications and Information Administration, nor does it imply that the equipment or software identified is necessarily the best available for the particular application or uses.

For questions or information on this or any other NTIA scientific publication, contact the ITS Publications Office at ITSinfo@ntia.gov or 303-497-3572.

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