To consider spectrum requirements and possible regulatory actions, including allocations, in order to support the safe operation of unmanned aircraft systems (UAS), based on the results of ITU-R studies, in accordance with Resolution 421 (WRC 07).
The relevant band is 5030-5150 MHz Aeronautical Radionavigation Service (ARNS) (microwave landing systems).
The primary concern for radio astronomy is the potential for out-of-band emission from transmitters in the 5030-5150 MHz band causing interference in the primary RAS allocation 4990-5000 MHz and the secondary Radio Astronomy Service (RAS) allocation 4800-4990 MHz. Nearly all centimeter-wavelength radio telescopes operate in the 4800-5000 MHz band to study the continuum radio emission from stars, galaxies, quasars, gamma-ray bursts, and other sources of galactic and extragalactic thermal and nonthermal continuum radiation. Aircraft pose a special problem for ground-based radio astronomy facilities because there is a line-of-sight path out to hundreds of kilometers.
A one-watt equivalent isotropically radiated power (EIRP) transmitter located 25 km (line of sight) from a radio astronomy facility needs to have its total out-of-band emissions in the RAS band under –72 dBc to conform to the continuum level specified in Recommendation ITU-R RA.769—that is, an average power density of less than –171 dBW/m2 in 10 MHz. It must also limit narrow band spurs to peaks no more than 11 dB above this average level in any 50 kHz channel within the RAS band, in order to conform to the corresponding spectral line level of –230 dBW/m2/Hz specified in Recommendation ITU-R RA.769.
Recommendation: Transmissions in support of unmanned aircraft in the 5030-5150 MHz band should have sufficiently low level of unwanted emissions to avoid interference in the adjacent Radio Astronomy Service bands, in accord with Recommendation ITU-R RA.769.