Pulse-Doppler is a radar system capable of not only detecting target location (bearing, range, and altitude), but also measuring its radial velocity (range-rate). It uses the Doppler effect to determine the relative velocity of objects; pulses of RF energy returning from the target are processed to measure the frequency shift between carrier cycles in each pulse and the original transmitted frequency. To achieve this, the transmitter frequency source must have very good phase stability and the system is said to be coherent.
The nature of pulsed radar, and the relationship between the carrier frequency and the pulse repetition frequency (PRF) means that the frequency spectrum can be very complex, leading to the possibility of errors and tradeoffs. In general, it is necessary to utilise a very high PRF to avoid aliasing, which can cause side effects such as range ambiguity. To avoid this, multiple PRFs are often used.
The maximum velocity that can be unambiguously measured is inherently limited by the PRF, as discussed above. The PRF-value must therefore be chosen carefully, based on a tradeoff between maximum velocity resolution and the reduction of velocity aliasing and range ambiguity problems. This tradeoff is highly application dependent, as e.g. weather radars measure velocities at a totally different scale as compared to radars designed to detect supersonic missiles and aircraft.
Stationary targets such as earth ground clutter (land, buildings, etc) will be dominant in the low doppler frequencies, while moving targets will produce much higher doppler shifts. The radar processor can be designed to mask out clutter by the use of doppler filters (digital or analogue) around the main spectral line (called the clutter-notch), which will result in the display of moving targets only (in relation to the radar). If the radar itself is moving, such as on a fighter aircraft, or a surveillance aircraft, then much more processing will be required, as the clutter in the filters will be based on platform speed, terrain under the radar, antenna depression angle, and antenna rotation/steered angle.
For Doppler Effect read this:
http://en.wikipedia.org/wiki/Doppler_effect
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These are the details about the radar that's gonna be fit into the upgraded Mirages of the IAF:
Frequency:8 to 12 GHz
Range: 160km
Band: I/J
Retrieved from "http://en.wikipedia.org/wiki/RDY_(Radar_Doppler_Multitarget)"
Central to the upgraded multirole capability of the Dash 5 is the RDY radar developed by Thomson-CSF/Detexis. Development of the RDY radar began in 1984 and the programme proceeded smoothly. In July 1987 the first of nine prototypes took to the air in a Falcon 20, and seven years later in December 1994, Thomson-CSF were able to deliver the first production standard set. RDY is the result of Thomson-CSF's experience gained from producing four generations of fighter radar, in particular the RDI radar -the first Pulse Doppler radar developed by Thomson-CSF.
The RDY can select one of three PRF (Pulse Repetition Frequency) modes, namely low, medium and high when operating in the air intercept mode (Auto Waveform Management). Low PRF is employed in the Look - Up mode. High PRF is best suited to long range Look - Down, while Medium PRF is used at all altitudes due to its reliable target detection properties. Thomson - CSF have developed algorithms that continually optimise the wave form to guarantee the highest target discrimination, even when the enemy is using advanced ECM. RDY has proved its ability to accurately measure target range even in heavy ground clutter and consistently demonstrates a “False Alarm Rate” of zero. When operating in the air-to-ground mode, the RDY employs Doppler Beam Sharpening, terrain mapping and air-to-ground ranging. RDY can simultaneously detect 24 airborne targets, irrespective of their altitude, track the eight most threatening and auto-prioritise four of them. Thomson-CSF/Detexis quote the look-up, look-down, shoot-up, shoot-down performance as being 70 km. In actual practice engagements conducted by the French AdlA, RDY has demonstrated its ability to detect, reliably, fighter size targets at 140 km. Great effort has been made reduce the effectiveness of any ECM that the enemy might choose to employ. Of significance is the advanced signal processing and the Monopulse receiver with its three independent channels. The RDY is however being developed further. The latest version, RDY-2 has a 15% greater air-to-air range, a SAR (Synthetic Aperture Radar) mode that allows ground mapping with a resolution of less than one metre and refined moving ground target tracking.
RDY is the standard fit on the Mirage 2000-5,-5Mk2 (enhanced RDY) and -9 (enhanced RDY) aircraft and has been retrofitted aboard 37 French Air Force Mirage 2000Cs (aircraft to Mirage 2000-5F standard; 11 aircraft redelivered during 1998, 22 during 1999), 25 Greek Mirage 2000EG and 62 United Arab Emirates' Mirage 2000EAD/DADs. Other identified offshore customers for the Mirage 2000-5 comprise Qatar (Mirage 2000-5EDA and -5DDA aircraft) and Taiwan (Mirage 2000-5Ei and -5Di aircraft).