be short enough to detect fine scatterers without
sacrificing severe weather detection abilities.
Amplitude
Wave amplitude is simply the wave’s height (from
the midline position) and represents the amount of
energy or power contained within the wave. Simply
put, greater amplitude means more power. Amplitude
is usually expressed as some fraction of a meter (fig.
2-5).
Frequency
Frequency refers to the number of completed wave
cycles per second. Radar frequency is expressed in
units of hertz (Hz); one hertz being equal to one cycle
per second. Frequency and wavelength are closely
related as a change in one has a direct impact on the
other. Essentially, higher frequency transmitters
produce shorter wavelengths and lower frequency
transmitters produce longer wavelengths. All wave
characteristics in some way affect radar power. When
more energy is available to strike targets, both signal
strength and data reliability are increased and the radar
performs more efficiently.
Electromagnetic waves can be described in terms
of either frequency or wavelength. Looking back at
figure 2-2, you can see the function of frequency
versus wavelength.
Power
Power is the rate at which energy is used, With
electromagnetic energy, the decibel system is used to
compare two power values. A decibel, abbreviated
"dB” is one tenth of a bel, the fundamental unit. The
decibel system is useful for comparing power values
that differ greatly, such as transmitter and receiver
power. Values for dB are measured logarithmically,
not linearly. With this in mind, you must be aware that
every change of 3 dB corresponds to a doubling (or
halving) of power. Doppler reflectivity values, which
will be discussed later, are indicated by the
abbreviation "dBZ."
Q1.
Q2.
Q3.
Q4.
Q5.
Q6.
Q7.
REVIEW QUESTIONS
What is an electromagnetic wave?
Radar energy occupies what portion of the
electromagnetic spectrum?
Wavelength is usually measured in what units?
How does wavelength affect a radar’s ability to
detect different types of targets?
Define radar frequency.
Given a frequency of 200 MHz and a frequency
of 100 GHz, which one has a shorter
wavelength?
How can different radar power values be
compared?
BASIC RADAR CONFIGURATION
LEARNING OBJECTIVES:
Define
reflectivity. Identify the major parts of a radar
system. Define radar sensitivity.
The acronym RADAR stands for RAdio Detection
And Ranging. Radio waves, like light waves, are
reflected from objects. The term reflectivity refers to
the amount of energy returned from an object and is
dependent on the size, shape, and composition of the
Figure 2-5.—Amplitude of an electromagnetic wave.
2-4
