Radars are quite prominent in the field of military reconnaissance and enemy detection or presence. The word “radar” is an abbreviation of the word radio detection and ranging. Its inception can be traced back to 1926, when Breit and Tuve observed the reflection of short-wave radio signals back from the ionized upper layer of the earth’s atmosphere. This technique was developed extensively during World War II in the early 1940s and became one of the leading surveillance equipment for any aircraft or submarine that comes near them. Radar waves are electromagnetic in nature, thus they travel at the speed of light. Thus the echo that will be received can more or less pinpoint the location of the entity even if it’s moving at great speeds.
There are two categories of radars: continuous-wave and pulsed radars. Continuous-Wave radars are so named because they transmit almost all the time. Under this category is Doppler radar frequency-modulated radar. Doppler radar operates continuously at a given frequency wherein the detection of target is accomplished using the Doppler principle. Any reflecting object waving toward or away from the transmitter will return echo signals slightly different in the frequency from the transmitted frequency due to Doppler shift. Frequency modulated radar is similar to a Doppler radar but uses a frequency-modulated signal. It also has the advantage of determining the range of moving and stationary targets. Pulsed radars transmit energy in the form of short bursts RF energy. Following the initial transmission, a certain amount of “listening” time is allowed for the reception of any reflected signals; if any echo is received, elapsed time is used to measure range. There are two types of pulse radars: primary and secondary radars. Primary pulsed radars refer to the simple echo system and elapsed time used to calculate range. It has the disadvantage of requiring a large reflecting object to yield enough echo for calculation. Secondary pulsed radar is a development of the primary to address its limitation of not supplying positive identification of targets.
Posted 2011-01-29 and updated on Jun 07, 2011 11:49pm by crisd