Frequency-Sharing and Spread-Spectrum Transmission with Large Relative Bandwidth

Radio transmission has been based traditionally on the concept of a small relative frequency bandwidth, which permits the use of circuits and structures that resonate with sinusoidal functions. This approach created no problems until high-resolution radar advanced to pulse durations in the order of 1 ns, and spread-spectrum transmission to frequency bands in the order of 100 MHz. The use of a small relative frequency bandwidth requires in these cases operation at frequencies above 10 GHz. Absorption by rain and fog as well as the high noise temperature, make these high frequencies less desirable. Furthermore, the lower frequency bands cannot be used, even though they are there and their absolute bandwidth is perfectly sufficient; only the unnecessary requirement of a small relative bandwidth prevents their use. Concepts and equipment that allow operation with a large relative bandwidth make it possible to operate radar with a resolution up to 0.1 ns in the most desirable range from a few hundred megahertz to about 10 GHz; spread-spectrum transmission can operate without regard to the relative frequency bandwidth. This paper explains primarily the motivation for the development of equipment handling large relative bandwidths, since the equipment itself has already been discussed in the literature and is available on an advanced experimental level.