Radar Height Estimation via Particle Filter Multipath Analysis
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Solution Overview
Problem
Existing radar systems face challenges in accurately estimating the height of a target over a reflective surface due to multipath errors, which are exacerbated by the need for narrow beamwidths, complex angle techniques requiring prior knowledge of reflection parameters, and biased estimates at low signal-to-noise ratios.
Innovation Solution
A multibeam radar system that uses a particle filter algorithm to estimate the target height without prior knowledge of the reflection coefficient or phase shift, allowing the antenna to remain pointed at the target in both free space and multipath modes, and can be implemented as software in existing systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a narrow beamwidth is used to reduce multipath errors, then target height estimation accuracy is improved, but beamwidth cannot be made narrower due to technical limitations and other radar functions require wider beamwidth
Solution Approach 1:
The radar system segments the received signal into direct path component and multipath component based on their different propagation characteristics. By separating these components through signal processing rather than physical beam narrowing, the system achieves accurate height estimation without constraining the antenna beamwidth
Solution Approach 2:
The invention changes the approach from spatial parameter (beamwidth) to signal parameter (complex ratio analysis). By analyzing the complex ratio of monopulse signals and detecting quadrature components, the system transforms the physical constraint problem into a signal processing problem that can be solved without narrowing the beam
2Measurement precision
If complex angle techniques are used to detect multipath, then height estimation accuracy is improved, but prior knowledge of reflection parameters and surface geometry is required which is generally not available
Solution Approach 1:
The radar system uses its own transmitted signal as the reference for detecting multipath effects. By comparing the received signal characteristics with the known transmitted signal, the system self-determines the multipath presence and characteristics without requiring external information about reflection parameters or surface geometry
Solution Approach 2:
The invention introduces the complex ratio of monopulse signals as an intermediary measurement that indirectly reveals multipath information. This intermediary allows the system to detect quadrature components that indicate multipath without directly measuring reflection parameters or surface properties
3Reliability
If symmetric beam ratio concept is used to eliminate multipath errors, then multipath errors are eliminated, but at least three beams are required and switching problem between pointing modes is introduced
Solution Approach 1:
Instead of trying to eliminate multipath by symmetric beam ratio as in conventional approaches, the invention inverts the approach by using the quadrature component of the complex signal ratio to directly detect and measure multipath effects. This allows the system to work with the multipath rather than trying to eliminate it through complex beam configurations
Solution Approach 2:
The invention extracts the multipath information from the quadrature component of the complex monopulse signal ratio. By separating and analyzing this specific component, the system isolates the multipath effect without requiring multiple beams or mode switching mechanisms
4Reliability
If track filtering is applied to mitigate multipath errors, then some errors are reduced, but stochastic characterization of elevation angle error is difficult resulting in lack of accuracy
Solution Approach 1:
The system performs preliminary detection of multipath conditions by analyzing the quadrature component of the complex signal ratio before final height estimation. This preliminary action allows the system to identify and correct for multipath effects in advance, improving the accuracy of subsequent elevation angle measurements without relying on difficult stochastic characterization
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 provides accurate target height estimation across various ranges with reduced multipath errors, maintaining antenna pointing consistency and being cost-effective by eliminating the need for dedicated devices.
Implementation Method 1
an indirect surface-reflected signal
Implementation Method 2
tracking radars
Data Source
Figure 1
Figure 2
AI summary
There is disclosed an apparatus for estimating the height at which a target flies over a reflective surface. The apparatus comprises means for emitting a signal, means for receiving signals, including the emitted signal after it has been echoed by the target, and means for filtering the received signals. The apparatus also comprises means for modeling a direct signal coming directly from the target after the emitted signal has been echoed by the target. The apparatus also comprises means for modeling an indirect signal coming indirectly from the target after the emitted signal has been echoed by the target and has been reflected by the surface, based on reflection parameters. The means for filtering estimate dynamically the reflection parameters. Application : tracking radars, surveillance radars, GPS