Spectrum Access for the Passive Services: The Past and the Future

The radio astronomy service (RAS), Earth exploration satellite service (passive) [EESS (passive)], and space research service (passive) [SRS (passive)], collectively known as the passive services, have unique spectrum requirements. Radio astronomy requires access to the spectrum at approximately octave intervals for continuum observations, and in addition to a large number of spectral lines that provide unique information about specific physical processes. The EESS, known more commonly as satellite remote sensing, has somewhat similar requirements. Due to the similarities, and because the passive services are much more sensitive to interference than active communication services, they have been mostly co-allocated and some bands have been allocated to them on an exclusive, primary basis. When looked at closely, however, the RAS and EESS (passive) requirements differ in terms of geographic location, timing, and other details. As the radio spectrum becomes increasingly congested, sharing on a band-by-band basis between active and passive services becomes increasingly difficult. This paper discusses how sharing between the passive services, particularly radio astronomy, and the active services evolved, and some of the issues the RAS and EESS community must resolve.