object. Through short bursts of radio EM energy,
weather radar equipment displays the location and
intensity (reflectivity) of meteorological targets such
as rain showers and thunderstorms.
Figure 2-6 is a block diagram for a simple radar
system that consists of the following components:
A modulator that tells the transmitter when to
transmit and for what duration.
A transmitter that generates power.
An antenna that concentrates the radiated power
into a shaped beam, which points in the desired
direction and collects the echo signal for delivery to the
receiver.
A duplexer that connects the transmitter to the
antenna during the transmission of the radiated pulse
and connects the receiver to the antenna during the time
between radiated pulses.
A receiver that amplifies the weak echo signals
picked up by the antenna to a level sufficient to display
them.
A signal processor that evaluates the signal from
the receiver.
A visual display unit that presents the
information contained in the echo signal to an operator
for interpretation.
Of prime importance concerning all these
components is the radar’s sensitivity. A radar’s
sensitivity, or signal to noise ratio, is a measure of the
interference generated by the radar (self noise) against
the minimum signal it is able to detect.
REVIEW QUESTIONS
Q8. What is meant by the term "reflectivity"?
Q9.
Which part of a radar system shapes energy into
a beam?
Q10.
What is meant by the term "radar sensitivity "?
PRINCIPLES OF RADAR
PROPAGATION
LEARNING OBJECTIVES: Distinguish
various radar pulse characteristics, including
pulse length, listening time, range ambiguity,
range folding, and pulse volume. Define range
resolution and pulse repetition frequency.
Compute Rmax. Recognize the effects of
beamwidth, beam broadening, and sidelobes on
radar energy. Define azimuthal and range
resolution.
Rather than transmit one long continuous wave
(CW), weather radar uses short, powerful bursts of
energy called pulses. Pulsed energy travels along a
focused path called a beam, and occupies a specific
amount of space. Pulses are separated by silent periods
that allow the antenna to listen for a return pulse. The
information gained from these pulses is critical in
Figure 2-6.—Block diagram for a simple radar system.
2-5
