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Radar Pulse Train. The carrier is an RF signal, typically of microwave frequencies, which is usually (but not always) modulated to allow the system to capture the required data. In simple ranging radars, the carrier will be pulse modulated and in continuous wave systems, such as Doppler radar, modulation may not be required
Pulse compression is a signal processing technique commonly used by radar, sonar and echography to either increase the range resolution when pulse length is constrained or increase the signal to noise ratio when the peak power and the bandwidth (or equivalently range resolution) of the transmitted signal are constrained.
The first operational pulse-Doppler radar was in the CIM-10 Bomarc, an American long range supersonic missile powered by ramjet engines, and which was armed with a W40 nuclear weapon to destroy entire formations of attacking enemy aircraft. [1] Pulse-Doppler systems were first widely used on fighter aircraft starting in the 1960s. Earlier ...
The range and velocity of a target are detected through pulse delay ranging and the Doppler effect (pulse-Doppler), or through the frequency modulation (FM) ranging and range differentiation. The range resolution is limited by the instantaneous signal bandwidth of the radar sensor in both pulse-Doppler and frequency modulated continuous wave ...
Doppler signals fall between 1.5 kHz, and 15 kHz, which is audible, so audio signals from medium-PRF radar systems can be used for passive target classification. For example, an L band radar system using a PRF of 10 kHz with a duty cycle of 3.3% can identify true range to a distance of 450 km (30 * C / 10,000 km/s).
A Barker code resembles a discrete version of a continuous chirp, another low-autocorrelation signal used in other pulse compression radars. The positive and negative amplitudes of the pulses forming the Barker codes imply the use of biphase modulation or binary phase-shift keying; that is, the change of phase in the carrier wave is 180 degrees.
Monopulse radar is a radar system that uses additional encoding of the radio signal to provide accurate directional information. The name refers to its ability to extract range and direction from a single signal pulse. Monopulse radar avoids problems seen in conical scanning radar systems, which can be confused by rapid changes in signal strength.
AN/APN-81 Doppler radar navigation system, mid-1950s. Doppler radar tends to be lightweight because it eliminates heavy pulse hardware. The associated filtering removes stationary reflections while integrating signals over a longer time span, which improves range performance while reducing power. The military applied these advantages during the ...