Monopulse radar is a type of Radar that determines the angular position of a target from a single Pulse by comparing signals from multiple simultaneous antenna beams. This allows precise angle measurement without requiring multiple pulses. The principle is analogous to how humans localize sound: by comparing the signals arriving at two ears, the left and right channels, the brain determines the direction of the source.
Sum Channel
The sum channel () is the coherent sum of signals from the left () and right () halves of the antenna. It provides maximum gain on boresight and is used for range, Doppler, and general detection processing.
Difference Channel
The difference channel () is the coherent difference between signals from the two halves of the antenna. It has a null on boresight and grows linearly with angular offset, making it sensitive to how far the target is from the beam center.
Error Ratio
The monopulse error ratio is , the difference channel normalized by the sum channel. This ratio is proportional to the angular offset of the target and is independent of target return strength.
Cross-Elevation and Elevation Error
Two difference channels are formed simultaneously, one for azimuth and one for elevation, providing 2D angular error in a single pulse.
Calibration Rotation
Phase and amplitude imbalances between the sum and difference channels introduce a bias in the error ratio. Calibration rotation corrects for this by applying a known complex rotation to align the channels.
Phase Coherence
The sum and difference channels must be phase-coherent, processed with the same local oscillator, for the error ratio to be valid.
AFC
Automatic Frequency Control (AFC) adjusts the local oscillator to keep the Receiver locked onto the target’s carrier frequency, maintaining phase coherence across pulses.