Guidance Signal Extraction in an ESA Based RF Seeker by Disturbance Observer

Extraction of guidance signal in a missile seeker involves filtering out the body (platform) motion component from the target sight line rate signal. In a strapdown seeker, there are no gimbals and the sensing frame is directly mounted on the missile base and consequently, there is virtually no mechanical isolation, which makes the filtering of platform motion signal challenging. This paper presents a disturbance observer (DOB) based scheme for guidance signal extraction in a missile seeker based on an onboard miniaturised Electronically Scanned Array (ESA) radar, where the electronically formed radar beam is steered in two axes to track the target. In the proposed filter, inspired by an earlier work on gimballed seekers, the guidance signal is extracted from the beam steering signal and the raw observer sight line rate signal. Effectiveness of the scheme to substantially reduce the disturbance component from platform motion is analysed and demonstrated. Sensitivity studies have been conducted on the proposed DOB-based estimator to validate its performance under a number of off-nominal conditions. In particular, robustness with respect to uncertainties in the monopulse angle channel measurement, the effect of beam control digitization and perturbation in parameters of the inertial measurement unit (IMU) has been characterized.