| 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 10GHz; 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.
8 pages. |