Virtual Aperture Radar Imaging for Missile Aimpoint
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Solution Overview
Problem
Radar imaging systems for airborne weapons face challenges in achieving high-resolution range and angle measurements during the terminal phase due to limited antenna aperture and Doppler resolution, leading to poor cross-range resolution and difficulties in aimpoint localization, especially with the 'glint' phenomenon and clutter interference.
Innovation Solution
The system employs sparse reconstruction techniques with an overcomplete array manifold parameterized by range or angle, exceeding the Rayleigh resolution bound, to uniquely identify scatterers and provide aimpoint updates without requiring large aperture antennas or training data, using a single pulse for radar imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a small physical antenna aperture is used in the terminal phase, then the weapon can maintain a compact size and rapid maneuverability, but cross-range resolution deteriorates due to the small aperture and co-alignment of range and Doppler contours
Solution Approach 1:
The patent transforms the radar imaging problem from traditional Doppler-based cross-range resolution to a sparse signal reconstruction problem in the spatial domain. By formulating the imaging as a sparse recovery task using a dictionary of possible scatterer configurations, the system achieves super-resolution without being constrained by the physical aperture size, effectively adding a new dimension of solution space beyond conventional Doppler processing.
Solution Approach 2:
The patent changes the fundamental parameters used for resolution from Doppler frequency (which is limited by aperture size) to sparse spatial coordinates of scatterers. By parameterizing the target scene in terms of discrete scatterer positions and reflectivities rather than continuous Doppler spectra, the system can achieve finer resolution than the Rayleigh limit imposed by the small antenna aperture.
2Loss of information
If Doppler processing is used for cross-range resolution, then velocity information can be obtained, but resolution deteriorates when Doppler shifts of scatterers at beam edges are nearly identical to those at the center
Solution Approach 1:
The patent introduces a sparse signal reconstruction algorithm as an intermediary between the raw radar measurements and the final cross-range resolution. Instead of directly using Doppler processing, the system uses the sparse recovery algorithm to infer scatterer positions from the measurements, effectively mediating the resolution process to overcome the Doppler aliasing problem while still utilizing the velocity information for range-Doppler coupling correction.
3Loss of time
If monopulse techniques are used for aimpoint determination, then single-pulse measurement is possible, but accuracy deteriorates due to the glint phenomenon causing wide apparent variations in target aimpoint
Solution Approach 1:
The patent performs preliminary action by formulating the aimpoint determination as a sparse reconstruction problem before actually solving for the scatterer positions. By pre-defining a dictionary of possible scatterer configurations and their corresponding radar signatures, the system prepares the measurement model in advance, allowing it to rapidly resolve the glint phenomenon through sparse recovery rather than relying on monopulse techniques that are sensitive to scatterer coherence changes.
4Measurement precision
If traditional synthetic aperture radar imaging is used, then high-resolution imagery can be obtained, but the weapon must be at a distance of 1.5-3 kilometers from the target, which limits the duration of the imaging stage
Solution Approach 1:
The patent replaces the mechanical requirement of large aperture or long integration time (as in traditional SAR) with a computational approach using sparse signal reconstruction. By substituting the physical aperture limitation with a mathematical reconstruction algorithm, the system can achieve high-resolution imagery in the terminal phase even with a small antenna and rapidly changing geometry, effectively replacing the mechanical SAR imaging process with a computational one.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables accurate resolution of multiple closely spaced or highly correlated scatterers, improving aimpoint localization and guidance precision by exceeding traditional resolution limits, even in rapidly changing geometries and cluttered environments.
Implementation Method 1
A radar imaging airborne weapon such as a missile, smart projectile etc. engaging a target
Implementation Method 2
a return pulse reflected off the multiple scatterers on the target is received
Implementation Method 3
A return pulse reflected off the multiple scatterers on the target is received and sampled at the antenna array to generate a data cube
Data Source
AI summary
Virtual Aperture Radar (VAR) imaging provides terminal phase radar imaging for an airborne weapon that can resolve multiple closely-spaced or highly correlated scatterers on a given target with a single pulse to provide an aimpoint update at a useful range to target without training data and without requiring a large aperture antenna. VAR imaging exploits the sparse, dominant-scatterer nature of man-made targets. The array manifold is constructed with a large number of basis functions that are parameterized by range or angle (or both) to target. The number of basis functions extends the capability to resolve scatterers beyond the Rayleigh resolution. However, this also makes the manifold underdetermined. A sparse reconstruction technique that places a sparsity constraint on the number of scatterers is used to solve the manifold to uniquely identify the ranges or angles to the scatterers on the target. These updates are passed to the weapon's guidance system, which in turn generates command signals to actuate aerodynamic surfaces such as fins or canards to steer the weapon to the target.