FMCW Radar Chirp Modulation for Spur-Resistant Detection
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Solution Overview
Problem
Frequency modulated continuous wave (FMCW) radar systems suffer from spurious tones (spurs) in their output signals, leading to false target detection due to artifacts resembling object reflections.
Innovation Solution
A modulation arrangement generates a sequence of chirps with varying transition period durations and frequency change rates to reduce spurious content in the radar signal, spreading spurs across frequencies and minimizing their impact on range-Doppler maps without additional processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a phase locked loop is used to generate the radar signal, then the radar signal can be generated with stable frequency tracking, but spurious tones appear in the output signal leading to false target detection
Solution Approach 1:
The patent applies dynamics by making the transition period duration variable rather than fixed. The modulation signal incorporates chirps with differently sized transition periods between active frequency sweeping and idle periods, which dynamically alters the phase locked loop's behavior to spread spurious tones across different frequencies, thereby reducing their harmful impact while maintaining frequency tracking stability
Solution Approach 2:
The patent changes the parameter of transition period duration in the modulation signal. By varying the length of transition periods between chirps in the sequence, the system modifies the frequency modulation characteristics to distribute spurious tones across the frequency spectrum, reducing their concentration and harmful effect on target detection
2Object-generated harmful factors
If transition periods are added between chirps to reduce spurs, then spurious content is reduced, but the signal processing complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-structuring the modulation signal with intentionally designed transition periods of varying durations before the signal enters the phase locked loop. This preliminary modification to the modulation waveform proactively prevents spurious tone concentration, eliminating the need for complex post-processing to remove spurs, thereby reducing overall system complexity
Data Source
AI summary
A mechanism for generating a modulation signal for use in a radar system. The modulation signal includes a sequence of chirps. Each chirp includes an active period, a transition period and an idle period. During the active period, the frequency of the chirp moves from a start frequency to an end frequency. During the transition period, the frequency of the chirp moves towards the start frequency of the next chirp. The rate of change of the frequency, during the transition period, is different for different chirps of the modulation signal.