RADAR is an acronym which stands for Radio Detection And Ranging. Several developments with respect to vacuum tube technology led up to the first practical application of radar in World War Two and it played a key role in the Battle of Briton. In contrast, had the radar returns of Japanese planes approaching Pearl Harbor on December 7, 1941 been taken seriously, the attack would not have been such a surprise and the outcome may have been quite different. Radar systems involve some of the most sophisticated innovative and dynamic electronics circuitry ever developed.
Radar systems consist of four basic subsystem components, the transmitter, antenna, receiver and Planned Position Indicator (PPI). The transmitter develops a pulse or burst of Radio Frequency (RF) energy—referred to as “main bang”— which is fed to the antenna. The antenna is designed to shape the RF pulse into a shaped beam and propagates it out into the air. When the RF pulse contacts an object down range from the radar, a small amount of the energy is reflected back at the radar. The radars antenna has a parabolic design which, like the mirror of an optical telescope, amplifies the returning RF and directs it into the receiver. The radar receiver further amplifies the reflected RF referred to as a “radar return” or simply a return. The amplified return signal is then displayed on a special type of cathode ray tube (CRT) called the PPI. Depending on the radars design, four attributes can be deduced with respect to a return, including its “azimuth position” (compass heading and relative position to the radar set), “range”(in miles from the radar), “speed” and “elevation.”
RF energy propagates through the air at just under the speed of light or about 6.18 nautical miles per microsecond. The time it takes for a radar pulse to travel out one mile and reflect back to the radar’s antenna, referred to as a “radar mile,” is 12.36 microseconds. This parameter is used to establish the range of a target from the radar. The azimuth is determined by the compass heading which the antenna is pointed toward when the pulse is transmitted. The radar actually transmits thousands of pulses per second, so, from an azimuth perspective many returns are received from a target each time it is swept by the radar. The radar “sweep” is the time that it takes a radar antenna to physically complete a full revolution, in the case of 360 degree azimuth antennae, or scan up and down or side to side in the case of directional sweep antennae. The radar sweep can also be produced electronically using a fixed position antenna.
The radar’s receiver must be precisely tuned to amplify only the transmitted frequency and synchronized with the transmitters main bang to establish accurate range data. The positional telemetry from the antenna is equally critical in establishing accuracy. The composite radar signal is fed to the PPI display which generates a representation of the radars beam and sweep. The PPI also inserts accurate range marks based on timing circuits, as well as other application specific information useful to the radar operator.
The foregoing description provides a basic overview of the principles and apparatus that most radar systems employ. There are many other sophisticated electronic techniques incorporated in radar systems to establish system unique attributes, but all radar systems basically operate the same way, by propagating an RF pulse and then processing the reflected return to establish position, range and elevation, or in the case of ground penetrating radar, depth.
This article’s author is an electronics engineer holding a radar certification and the information presented in this article is based solely on the author’s expertise in the field. This information is provided in compliance with Helium source reference requirements.