INTRODUCTION
The transmitter is the subsystem of the radar that produces the short
duration, high-power RF pulses of energy that are focused and radiated into
space by the antenna. The history of the practical radar transmitter began
in 1940 when Great Britain developed a successful cavity magnetron.
This
made it possible to generate substantial amounts of power at microwave
frequencies. During that year, samples of the cavity magnetron were brought
to the Radiation Laboratory at Massachusetts Institute of Technology, where
research and development work was started in the microwave field. The term
RADAR is an acronym from the expression Radio Detection and Ranging.
The
heart of the radar system is the transmitter.
Two main types of
transmitters are now in common use. The first is the keyed-oscillator type.
In this transmitter, one stage or tube, usually a magnetron, produces the RF
pulse.
The oscillator tube is keyed by a high-power DC pulse of energy
generated by a separate unit called a modulator.
The second type of
transmitter consists of a power-amplifier chain.
This transmitter system
begins with an RF pulse of very low power.
This low-level pulse is then
amplified by a series of power amplifiers to the high level of power desired
in a transmitter pulse. In most power-amplifier transmitters, each of the
power-amplifier stages is pulse modulated in a manner similar to the
oscillator in the keyed-oscillator type.
This subcourse is designed to
familiarize you with the radar transmitters and systems associated with RF
propagation.
ix
Previous Page
