Where has all the spectrum gone?

The RF spectrum, from below 1 MHz to above 100 GHz, represents a precious and strictly finite resource. It is used for a wide range of purposes including communications, radio and television broadcasting, radionavigation, and radar. All users have a need for greater bandwidth. As the demand from all of these users continues to grow for more access to spectrum, there is ever-greater competition for this resource. Radar represents a fundamentally important use of the EM spectrum, in applications which include Air Traffic Control, marine navigation, geophysical monitoring of Earth resources from space, automotive safety, weather tracking, as well as numerous applications in defence and security. The purpose of this paper is to explain the nature and severity of the spectrum congestion problem, and to describe a number of possible approaches to its solution, both from regulatory and technical points of view.