DDS Phase Variation for Radar Spur Noise Reduction
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Solution Overview
Problem
Radar systems using Direct Digital Synthesizers (DDS) face issues with frequency spurs and noise accumulation, particularly in CW radar systems, which degrade detection capabilities by increasing the noise floor and making it difficult to detect smaller targets.
Innovation Solution
The system employs a DDS to generate a series of signals with similar primary frequency characteristics, where the starting phase or clock frequency is changed between each signal, ensuring that frequency spurs have different phases and are not accumulated during coherent integration, thereby reducing their impact on the noise floor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a DDS is used to generate modulated signals for transmission, then signal generation flexibility and precise control are improved, but frequency spurs appear on the DDS output which modulate the LO and increase the apparent noise floor
Solution Approach 1:
The patent applies periodic action by changing the starting phase of the DDS in a periodic manner across successive frequency sweeps. The phase is incremented by a fixed amount (e.g., 360 degrees divided by the number of sweeps) for each sweep, creating a systematic periodic variation that causes spurs to shift positions during integration, thereby reducing their cumulative effect on the noise floor.
Solution Approach 2:
The patent implements parameter changes by dynamically adjusting the starting phase parameter of the DDS between successive signal generations. This parameter modification causes the frequency spurs to appear at different relative positions in the integrated signal, preventing them from accumulating coherently and thus reducing their detrimental impact on detection sensitivity.
2Measurement precision
If coherent integration is used to improve signal to noise ratio, then detection capability is improved, but spurs present on the DDS output accumulate during integration and increase the apparent noise floor
Solution Approach 1:
By systematically varying the DDS starting phase across integration periods, the patent ensures that spurs appear at different positions in the frequency domain during coherent integration. This periodic phase modulation causes spur energy to smear out rather than accumulate, allowing coherent integration to improve signal-to-noise ratio without proportionally increasing the noise floor from spur accumulation.
Solution Approach 2:
The patent changes the phase parameter of the DDS between successive signals being integrated. This parameter variation ensures that while the desired signal components add coherently (improving signal-to-noise ratio), the spur components do not align and therefore do not accumulate constructively, preventing excessive noise floor elevation.
3Stability of the object's composition
If the same starting phase is used for each signal in an integration period, then signal coherence is maintained, but frequency spurs remain at the same position and accumulate during integration
Solution Approach 1:
The patent applies local quality by making different parts of the signal generation process have different phase characteristics. Specifically, each frequency sweep or signal within the integration period uses a locally different starting phase offset, while maintaining the same primary frequency characteristics. This localized phase variation prevents spur accumulation at any single frequency position while preserving overall signal coherence for target detection.
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 effectively reduces the noise floor by smearing out spurs during integration, improving the detection of smaller targets and enhancing the signal-to-noise ratio in radar systems.
Implementation Method 1
a direct digital synthesiser (DDS) for signal generation or processing
Implementation Method 2
the derived signals being comprised of intermediate frequency (IF) signals produced by mixing each signal with a delayed version of itself
Data Source
AI summary
A DDS based system, such as a radar, includes means for generating a plurality of transmission signals using a DDS, and means for integrating signals derived therefrom, such as received signals. The system further includes means for varying the relative starting phase of the plurality of transmission signals, or adjusting the DDS input clock while maintaining similar primary output frequency characteristics of the transmission signals. The approach has the effect of changing the location of unwanted frequency spurs in each of the transmission signals, and hence the effects of these are decreased in the integration process. An improvement in the sensitivity of the system results. Although primarily suited to radar applications the invention may find utility in other systems such as sonar or lidar systems.