Radar DC Offset Modulation for Spur Suppression
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Solution Overview
Problem
Radar systems face difficulties in distinguishing between internally generated spurs and low-power reflections from small or distant objects due to frequency spurs generated by the receive path having amplitudes similar to those of small or distant targets, leading to reduced sensitivity and accuracy.
Innovation Solution
The implementation of a method that involves downconverting reflected radar signals and adding different DC offsets during different chirp time periods, followed by digitization using an analog-to-digital converter, which shifts spur frequencies and reduces the magnitude of spur-induced 'ghost targets, thereby enhancing the signal-to-noise ratio and detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If frequency spurs are generated by the radar's receive path, then the radar system can operate with standard circuitry, but the radar system has difficulty distinguishing internally generated spurs from low power reflections from small or distant objects
Solution Approach 1:
The patent applies periodic action by alternating the DC offset value between different chirp periods. The DC offset circuit switches between a first DC offset value during first chirp periods and a second DC offset value during second chirp periods. This periodic variation causes frequency spurs to shift positions in the frequency domain across different chirps, allowing the radar system to distinguish between stationary spurs and actual target reflections through signal processing techniques that analyze consistency across multiple chirps.
2Reliability
If frequency spurs have amplitude on the same order of magnitude as frequency content from small or distant objects, then the radar system can maintain high sensitivity, but the radar system cannot distinguish spurs from actual targets
Solution Approach 1:
The patent uses periodic variation of the DC offset to cause frequency spurs to shift positions across different chirp periods. Since actual target reflections remain at consistent frequency positions relative to the transmitted signal, while spurs shift due to the DC offset changes, signal processing can identify and eliminate spurs by looking for inconsistent frequency positions across chirps, thereby maintaining sensitivity to weak targets while removing spur interference.
Solution Approach 2:
The patent converts the harmful effect of frequency spurs into a beneficial detection mechanism. By intentionally varying the DC offset, the system causes spurs to shift positions in a predictable manner, while legitimate target signals remain stable. This transforms the previously harmful spur interference into a useful signature that helps the signal processing algorithm distinguish between false artifacts and real targets, effectively converting a system defect into a detection advantage.
3Measurement precision
If different DC offsets are added during different chirp time periods, then spur frequencies are shifted and detection accuracy is improved, but the system complexity increases
Solution Approach 1:
The patent implements parameter changes by dynamically adjusting the DC offset value in the baseband signal path. A DC offset circuit receives a control signal that indicates which DC offset value to apply, switching between different offset values based on the chirp period. This parameter modulation of the DC offset enables spur suppression and improved detection accuracy while maintaining a relatively simple circuit implementation that can be integrated into existing radar architectures.
Data Source
AI summary
A method includes: receiving a reflected radar signal including a first radar chirp signal during a first chirp time period and a second radar chirp signal during a second chirp time period; downconverting the reflected radar signal to form a baseband signal; adding a DC offset to the baseband signal to form a DC offset baseband signal, adding the DC offset including adding a first DC offset to the baseband signal during the first chirp time period, and adding a second DC offset to the baseband signal during the second chirp time period, where the first DC offset is different from the second DC offset; and digitizing the DC offset baseband signal using an analog-to-digital converter to form a digitized baseband signal.