TABLE OF CONTENTS This chapter discusses pulse shapes, with their influence on spectra, and stability. The wavelengths used vary from millimeters to meters. Initially radar designers were pleased to have all the power that their magnetron could give reliably to illuminate the space around them. Today, the radar bands are crowded so that sidebands must be held to a minimum, and modern signal processing requires very stable transmitters.
Although continuous wave radars are used by the police to measure vehicle speeds, in most cases the transmitter signal is modulated to be able to measure the echo time and thus range. This modulation may be
| Frequency modulated; Phase modulated; |
| No modulation inside the pulse; Frequency modulation inside the pulse; Phase modulation inside the pulse. |
The majority of radars use pulse modulated transmitters. Early radars used triode or tetrode transmitters, sometimes self- oscillating until they were superseded by magnetrons during the Second World War. Greater stability and bandwidth are provided by klystron and traveling wave tube output stages, which came later in the more expensive military radars.
The transmitter power is a major factor in the radar range equation. Just as with a searchlight, the greater the power, the greater the range. Power in the microwave bands is expensive and inefficient to generate, so it must not be wasted. The range equation uses the transmitter energy or power times the pulse width. This represents the energy in each pulse. With shaped pulses, either or both the peak...
