Definition
There are two different types of radar scalloping. * Intra-pulse * Inter-pulseIntra-pulse Scalloping
This occurs when the radial velocity of the target induces a phase shift near 360 degree within the reflected pulse, which induces signal cancellation in the receiver. Intra-pulse radar scalloping begins to become a concern above the following velocity. : Scalloping occurs at 150 km/s for an L-band radar with a 1 microsecond pulse.Inter-pulse Scalloping
Inter-pulse radar scalloping involves two types of systems. * Moving Target Indicator * Pulse-Doppler RadarMoving Target Indicator
Scalloping occurs when the radial velocity of the reflector induces an integer multiple of a 360 degree phase shift between two or more transmit pulses. Radar scalloping for MTI radar begins to become a concern when the radial velocity is greater than the following value. : This occurs near multiples of 15 m/s for an L-Band radar withPulse-Doppler Radar
Scalloping for pulse-Doppler radar involves blind velocities created by the clutter rejection filter. A two PRF detection schemes will have detection gaps with a pattern of discrete ranges, each of which has a blind velocity. Scalloping happens in a two PRF detection scenario when target velocity produces a blind velocity for one PRF while the target is at the blind range of the other PRF. The blind velocity for a specific pulse repetition frequency (PRF) is an integer multiple of the following, which causes the signal to have zero doppler. : The blind range for a specific PRF is an integer multiple of the distance between transmit pulses, which is when the reflected pulse arrives at the same time as when the transmitter fires. : This leaves a series of detection gaps at discrete velocity and range combinations. These detection gaps are filled in by using three or more alternating PRF in the detection scheme. An L-Band transmitter using a 3 kHz and 4 kHz PRF pair has the following characteristics. * 3 kHz blind ranges are 50 km, 100 km, ... * 3 kHz blind velocities are 450 km/s, 900 km/s, ... * 4 kHz blind ranges are 37.5 km, 75 km, ... * 4 kHz blind velocities are 600 km/s, 1,200 km/s, ... This system would fail to detect reflections at 50 km and 100 km that are moving 600 km/s or 1,200 km/s. It would also fail to detect reflections at 37.5 km and 75 km that are moving 450 km/s or 900 km/s.Compensation Strategies
Intra-pulse scalloping is improved by shortening the transmit pulse or by modulating the transmit pulse. This can include frequency or phase shifting associated with