Digital Radar Signal Processing for Range Resolution
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Solution Overview
Problem
Radar and sonar systems face limitations due to the use of analog processing and control, which leads to sub-optimal filtering, aliasing issues, and redundancy in signal processing, particularly in handling multiple pulse widths and ranges, resulting in reduced range resolution and information loss.
Innovation Solution
Implementing a linear demodulation and anti-aliasing filter with sub-sampling analog-to-digital conversion, followed by digital signal processing, including matched filters and dynamic range compression, to enhance signal quality and enable simultaneous display of multiple range images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If analog processing and control are used in radar and sonar systems, then device complexity is reduced and manufacturing cost is lowered, but range resolution deteriorates and aliasing issues occur
Solution Approach 1:
The patent replaces analog signal processing mechanisms with digital signal processing systems. Specifically, analog filters are substituted with digital filters, and analog-to-digital conversion is performed early in the signal chain to enable digital processing of radar and sonar signals, thereby achieving superior range resolution and eliminating aliasing while maintaining manageable system complexity through integrated digital processors
Solution Approach 2:
The patent changes the fundamental parameter of signal representation from analog continuous form to digital discrete form. By performing analog-to-digital conversion at the input stage and using digital filters with precisely controllable bandwidths, the system achieves accurate range resolution without the limitations of analog filter drift and the aliasing problems inherent in analog processing
2Adaptability or versatility
If multiple pulse widths are used to optimize range resolution and power, then adaptability is improved, but device complexity increases due to multiple filters required
Solution Approach 1:
The patent implements a universal digital filtering approach where a single set of digital filters can process multiple pulse widths effectively. The digital signal processor can dynamically adjust filter parameters and apply matched filtering techniques that are optimized for each pulse width, eliminating the need for multiple physical analog filters while maintaining adaptability to different ranging requirements
Solution Approach 2:
The patent introduces dynamic filter parameter adjustment capability in the digital domain. The system can change filter bandwidth, center frequency, and other parameters in real-time based on the selected pulse width, allowing optimal filtering for each pulse configuration without requiring physical filter changes or multiple fixed filters
3Ease of manufacture
If analog logarithmic demodulation is used to generate baseband video, then manufacturing cost is reduced, but information is lost due to thresholding in comparators
Solution Approach 1:
The patent replaces the analog logarithmic demodulation and thresholding process with digital signal processing. By performing demodulation in the digital domain after high-resolution analog-to-digital conversion, the system preserves all signal information without the information loss caused by 1-bit comparator thresholding, while the overall manufacturing cost remains competitive due to the integration of digital processing functions
Solution Approach 2:
The patent creates a high-fidelity digital copy of the analog signal through precise analog-to-digital conversion before any processing occurs. This digital replica preserves the complete signal information, allowing for lossless processing, storage, and manipulation, in contrast to the irreversible thresholding that occurs in analog comparator-based systems
4Weight of moving object
If radar signal processors are placed in display apparatus rather than the scanner, then size and weight constraints on the scanner are satisfied, but redundancy occurs when multiple displays are used
Solution Approach 1:
The patent extracts the signal processing functions from the display apparatus and relocates them to the scanner unit. By integrating the digital signal processor directly in the scanner, the system eliminates redundant processors in multiple displays, as the centralised processor in the scanner serves all display units, reducing the total number of processors while maintaining lightweight scanner design
5Productivity
If sub-sampling analog-to-digital conversion is used, then productivity is improved by enabling simultaneous display of multiple range images, but aliasing may occur if not properly filtered
Solution Approach 1:
The patent applies anti-aliasing filtering in the digital domain immediately after sub-sampling analog-to-digital conversion, before any further signal processing occurs. This preliminary digital filtering removes aliasing components introduced by sub-sampling, allowing the system to achieve high productivity through simultaneous display of multiple range images without suffering from aliasing artifacts
Data Source
AI summary
A radar or sonar system amplifies the signal received by an antenna of the radar system or a transducer of the sonar system is amplified and then subject to linear demodulation by a linear receiver. There may be an anti-aliasing filter and an analog-to-digital converter between the amplifier and the linear receiver. The system may also have a digital signal processor with a network stack running in the processor. That processor may also have a network interface media access controller, where the system operates at different ranges, the modulator may produce pulses of two pulse patterns differing in pulse duration and inter-pulse spacing, those pulse patterns are introduced and used to form two radar images with the two images being derived from data acquired in a duration not more than twenty times larger than the larger inter-pulse spacing, or for a radar system, larger than one half of the antenna resolution time. One or more look-up tables may be used to control the amplifier. The radar system may generate digital output which comprises greater than eight levels of radar video.