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Angle Deception Jamming
Angle deception jamming is an electronic warfare technique used against conical scanning radar systems. It generates a false signal that fools the radar into believing the target is to one side of the boresight, causing the radar to "walk away" from the target and break its radar lock-on. It is also known as angle walk-off, angle stealing, or inverse con-scan. Angle stealing was one of the earliest jamming techniques to be used operationally, with systems employed against the German Würzburg radars near the end of World War II. The technique is not useful against monopulse radars, and is one of the main reasons those radars became popular in the post-war era. Angle stealing belongs to the wider class of "deceptive jamming" techniques, which attempt to deceive radars based on knowledge of their operating procedures, rather than simply trying to blind them with noise. Another popular deception technique that was used against early radars is range gate pull-off. Description Coni ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parabolic Reflector
A parabolic (or paraboloid or paraboloidal) reflector (or dish or mirror) is a Mirror, reflective surface used to collect or project energy such as light, sound, or radio waves. Its shape is part of a circular paraboloid, that is, the surface generated by a parabola revolving around its axis. The parabolic reflector transforms an incoming plane wave travelling along the axis into a spherical wave converging toward the focus. Conversely, a spherical wave generated by a point source placed in the focus (optics), focus is reflected into a plane wave propagating as a collimated beam along the axis. Parabolic reflectors are used to collect energy from a distant source (for example sound waves or incoming star light). Since the principles of Specular reflection, reflection are reversible, parabolic reflectors can also be used to collimate radiation from an isotropic source into a parallel beam (optics), beam. In optics, parabolic mirrors are used to gather light in reflecting telescop ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Automatic Gain Control
Automatic gain control (AGC) is a closed-loop feedback regulating circuit in an amplifier or chain of amplifiers, the purpose of which is to maintain a suitable signal amplitude at its output, despite variation of the signal amplitude at the input. The average or peak output signal level is used to dynamically adjust the gain of the amplifiers, enabling the circuit to work satisfactorily with a greater range of input signal levels. It is used in most radio receivers to equalize the average volume ( loudness) of different radio stations due to differences in received signal strength, as well as variations in a single station's radio signal due to fading. Without AGC the sound emitted from an AM radio receiver would vary to an extreme extent from a weak to a strong signal; the AGC effectively reduces the volume if the signal is strong and raises it when it is weaker. In a typical receiver the AGC feedback control signal is usually taken from the detector stage and applied t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IFF Mark II
IFF Mark II was the first operational identification friend or foe system. It was developed by the Royal Air Force just before the start of World War II. After a short run of prototype Mark Is, used experimentally in 1939, the Mark II began widespread deployment at the end of the Battle of Britain in late 1940. It remained in use until 1943, when it began to be replaced by the standardised IFF Mark III, which was used by all Allied aircraft until long after the war ended. The Mark I was a simple system that amplified the signals of the British Chain Home radar systems, causing the aircraft's "blip" to extend on the radar display, identifying the aircraft as friendly. MarkI had the problem that the Gain (electronics), gain had to be adjusted in flight to keep it working; in the field, it was correct only half the time. Another problem was that it was sensitive to only one frequency and had to be manually tuned to different radar stations. In 1939, Chain Home was the only radar o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Identification Friend Or Foe
Identification, friend or foe (IFF) is a combat identification system designed for command and control. It uses a transponder that listens for an ''interrogation'' signal and then sends a ''response'' that identifies the broadcaster. IFF systems usually use radar frequencies, but other electromagnetic frequencies, radio or infrared, may be used. It enables military and civilian air traffic control interrogation systems to identify aircraft, vehicles or forces as friendly, as opposed to neutral or hostile, and to determine their bearing and range from the interrogator. IFF is used by both military and civilian aircraft. IFF was first developed during World War II, with the arrival of radar, and several friendly fire incidents. IFF can only positively identify friendly aircraft or other forces. If an IFF interrogation receives no reply or an invalid reply, the object is not positively identified as foe; friendly forces may not properly reply to IFF for various reasons such as e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transponder
In telecommunications, a transponder is a device that, upon receiving a signal, emits a different signal in response. The term is a blend of ''transmitter'' and ''responder''. In air navigation or radio frequency identification, a flight transponder is an automated transceiver in an aircraft that emits a coded identifying signal in response to an interrogating received signal. In a communications satellite, a satellite transponder receives signals over a range of uplink frequencies, usually from a satellite ground station; the transponder amplifies them, and re-transmits them on a different set of downlink frequencies to receivers on Earth, often without changing the content of the received signal or signals. Satellite/broadcast communications A communications satellite’s channels are called transponders because each is a separate transceiver or repeater. With digital video data compression and multiplexing, several video and audio channels may travel through a single tr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phase Detector
A phase detector or phase comparator is a frequency mixer, analog multiplier or Digital logic, logic circuit that generates a signal which represents the difference in phase between two signal inputs. The phase detector is an essential element of the phase-locked loop (PLL). Detecting phase difference is important in other applications, such as electric motor, motor control, radar and telecommunication systems, Servomechanism, servo mechanisms, and demodulators. Types Phase detectors for phase-locked loop circuits may be classified in two types.Paul Horowitz and Winfield Hill, ''The Art of Electronics 2nd Ed. '' Cambridge University Press, Cambridge, 1989 pg. 644 A Type I detector is designed to be driven by analog signals or square-wave digital signals and produces an output pulse at the difference frequency. The Type I detector always produces an output waveform, which must be filtered to control the phase-locked loop voltage-controlled oscillator (VCO). A type II detecto ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amplitude Modulated
Amplitude modulation (AM) is a signal modulation technique used in electronic communication, most commonly for transmitting messages with a radio wave. In amplitude modulation, the instantaneous amplitude of the wave is varied in proportion to that of the message signal, such as an audio signal. This technique contrasts with angle modulation, in which either the frequency of the carrier wave is varied, as in frequency modulation, or its phase, as in phase modulation. AM was the earliest modulation method used for transmitting audio in radio broadcasting. It was developed during the first quarter of the 20th century beginning with Roberto Landell de Moura and Reginald Fessenden's radiotelephone experiments in 1900. This original form of AM is sometimes called double-sideband amplitude modulation (DSBAM), because the standard method produces sidebands on either side of the carrier frequency. Single-sideband modulation uses bandpass filters to eliminate one of the sidebands an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anti-aircraft Artillery
Anti-aircraft warfare (AAW) is the counter to aerial warfare and includes "all measures designed to nullify or reduce the effectiveness of hostile air action".AAP-6 It encompasses surface-based, subsurface (Submarine#Armament, submarine-launched), and air-based weapon systems, in addition to associated sensor systems, command and control arrangements, and passive measures (e.g. barrage balloons). It may be used to protect naval, army, ground, and air forces in any location. However, for most countries, the main effort has tended to be homeland defense. Missile defense, Missile defense is an extension of air defence, as are initiatives to adapt air defence to the task of intercepting any projectile in flight. Most modern anti-aircraft (AA) weapons systems are optimized for short-, medium-, or long-range air defence, although some systems may incorporate multiple weapons (such as both autocannons and surface-to-air missiles). 'Layered air defence' usually refers to multiple 't ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Conical Scanning
Conical scanning is a system used in early radar units to improve their accuracy, as well as making it easier to steer the antenna properly to point at a target. Conical scanning is similar in concept to the earlier lobe switching concept used on some of the earliest radars, and many examples of lobe switching sets were modified in the field to conical scanning during World War II, notably the German Würzburg radar. It was universal among gun laying radars by the end of WWII. Conical scanning uses the non-linear nature of the radar's antennas, which are most sensitive in a single direction. By rotating the antenna, the signal returned from the target will grow stronger and weaker depending on how close it is pointed to the target. By comparing the angle of the antenna to the signal strength and looking for a peak, the angle of the target can be determined, and by examining the shape of the returned signal over time, that angle can be measured with very high precision, on the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Half Power Point
The half-power point is the condition at which a system's output power has dropped to half of its peak value; that is, at a level of approximately . In filters, optical filters, and electronic amplifiers, the half-power point is also known as half-power bandwidth and is a commonly used definition for the cutoff frequency. In the characterization of antennas the half-power point is also known as half-power beamwidth and relates to measurement position as an angle and describes directionality. Amplifiers and filters This occurs when the output voltage has dropped to \tfrac \approx \text of the filter's nominal passband voltage and the power has dropped by half. A bandpass amplifier will have two half-power points, while a low-pass amplifier or a high-pass amplifier will have only one. The bandwidth of a filter or amplifier is usually defined as the difference between the lower and upper half-power points. This is, therefore, also known as the bandwidth. There is no lower hal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
