SubscribeThe radar concept is a very simple one: throw packets of energy (traveling at the speed of light) in a known direction and time how long it takes for echoes of those packets to get back.
Where no echo comes back there is nothing; where echoes come back there is something. That something can be a target of interest or an echo from the ground, a building, aircraft, person or other objects of no interest. Radar returns can be plotted (on a screen) or directly interpreted by a computer to yield target data.
RADAR is an acronym for "RAdio Detection and Ranging" but has become a word in its own right used and misused for various things such as, "They flew under the radar and won the contract."
Here's some terminology decoded for non-rocket (or radar) scientists.
Aperture
The size of the antenna. In general, for a given frequency, larger antennas are more efficient, sensitive and form tighter, more accurate beams.
Bearing
The angle from north (usually true north) to the target from the radar.
Clutter
Radar returns not important to a radar's function. If a radar is looking for walking people, competing returns from trees, fences, buildings, rainfall, etc. are called clutter.
False Alarm
Also known as a "False Positive," occurs when an alarm is generated but there is no target present. Most likely causes of false alarms are receiver noise and antenna sidelobes.
Frequency
As radar is a radio device, each radar type has a frequency (cycles per second) that it transmits at. This is like tuning the radio in your car, but usually at much higher frequency.
GHz
Giga (billions) Hz (cycle per second). Your car radio FM tuner has numbers like 97.7. Those are in Mega (millions) of Hz (MHz). Radar operates at higher frequencies, typically between 1 GHz and up to 100 GHz in narrow to wide channels of about 100 to 2000 MHz. The higher the frequency the more resolution, however, the maximum detection range is typically reduced by rainfall and, in extreme cases, humidity.
Jamming
Radars can be jammed (interfered with) by strong sources of radio energy. Some radars are designed to also act as jammers against other radars or radio receivers.
Microwave
A "catch-all" word to describe radio frequencies in the range of 1,000 MHz to 30,000 MHz. (1 GHz to 30 GHz). Most radars operate in some part of the microwave spectrum as do microwave ovens.
Millimeter-Wave
Radio frequencies in the range of 30 GHz to 300 GHz. Frequencies in this range have wavelengths ranging from 1 to 10 millimeters, hence 'millimeter-wave'.
Pulse Repetition Frequency
How often (per second) that pulses are "fired" at the target space.
Pulse Width
In radars that are pulsed, the pulse width is the duration of the "on" time of the pulse (in micro or nano seconds).
Radar Cross Section (RCS)
The apparent (to the radar) size of a target and is typically in square meters. It is not directly related to actual size. A hot air balloon has a low RCS and a small airplane can have a very large RCS. It depends on how much of the radar signal the target can reflect.
Radar Position
Where the radar is located, usually expressed in Latitude and Longitude. Some radar is mobile such as on ships, aircraft and vehicles.
Radar Scan
Since radars typically have a narrow beam, they have to scan the area of interest. This is done by turning the radar, antenna, scanning back and forth or in other patterns.
Radar Tracker
The part of the radar (electronics, software or usually both) that sifts through the radar signals to identify potential targets and to keep track of them.
Range
Distance, for example: how far a target is, how far the radar can detect a type of object, etc.
Sidelobes
The antennas that form the beam cannot be made economically or technically large enough to make a perfect beam so smaller "extra" beams may be formed beside, above and below the main beam. Targets that are detected in the sidelobes may be rejected in special software algorithms.
SNR (Signal to noiSe Ratio)
A measure of how clear a signal is received. The higher the SNR the better.
Tracking Threshold
In the presence of clutter and noise, a criteria is needed to separate targets from the environment around it. The tracking threshold (usually in "dB" or decibels) is the level required for a signal to be "above the noise" to be a candidate to be a target.
Target Position
Where a target is located. This can be expressed as a Range+Bearing from the radar or as a latitude/longitude (or other position reference). Knowing where the radar is located, one (or usually a computer) can compute the latitude and longitude of a target.
Transceiver
Transmitter + Receiver packaged as one unit and typically exchanging signals for timing and comparison.
Waveguide
A component of some radars that typically connects the antenna(s) to the transmitter and receiver.
Wavelength
The length of one cycle of the signal (usually in cm or meters). It is the speed of light divided by the radar frequency. As the frequency goes up, the wavelength gets shorter.
