Symmetrical difference pattern monopulse for low-angle tracking with array radar

Tracking low-elevation targets over a smooth surface is challenging because of the multipath effect. The symmetrical difference pattern monopulse is proposed for low-angle tracking with array radar. At first, the optimal symmetrical difference pattern is designed. The proposed monopulse is implemented using symmetrical sum and difference patterns by digital beam forming. The monopulse ratio derived from the symmetrical sum and difference patterns is not affected by the multipath effect. Then, the performance of the symmetrical difference pattern monopulse is evaluated by simulations in terms of the signal-to-noise ratio, target elevation, and complex reflection coefficient. Field data sets acquired from a VHF array radar are used for validation. It is found that the measurement error is still less than 1/30th of a beamwidth when the target elevation is less than a quarter of a beamwidth. The proposed monopulse scheme is suitable for VHF array radar, for which the multipath effect is serious.