Free-Running Oscillator Radar Phase Noise Reduction
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Solution Overview
Problem
FMCW radar systems face issues with phase noise, which leads to signal leakage and increased noise levels due to large static objects, affecting detection capabilities and system availability, and existing solutions either reduce detection capabilities or limit system availability.
Innovation Solution
A radar system using a free-running oscillator (FRO) as the local oscillator and a direct digital synthesizer (DDS) with a clock derived from the FRO, along with a coherent receive path, to generate signals with improved phase noise performance, especially at frequency offsets away from the carrier, and employing a quadrature up-conversion mixer to suppress unwanted sidebands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If transmit power is increased to improve detection range, then detection capabilities are improved, but noise levels increase due to phase noise multiplication
Solution Approach 1:
The patent changes the operational parameters of the local oscillator system by allowing it to run free at its natural frequency rather than being constrained by a PLL. This parameter change reduces phase noise at frequency offsets, which in turn reduces the noise multiplication effect when transmit power is increased, allowing higher power operation without proportional noise increases.
2Reliability
If detection threshold is raised to reduce false alarms, then false alarm rate is reduced, but detection capabilities are reduced
Solution Approach 1:
The patent converts the harmful effect of phase noise into a benefit by using a free-running oscillator whose natural phase noise characteristics actually improve overall system performance. The reduced phase noise at frequency offsets creates a cleaner signal environment that allows for better detection thresholds, converting what was previously a limiting factor into an advantage for detection capability.
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 reduces noise across all range bins, enhancing sensitivity and allowing increased transmit power without detrimental effects, thereby improving detection capabilities and range, especially for smaller radar cross-sectional area objects, and enabling coherent integration and better performance in adverse weather conditions.
Implementation Method 1
a free running oscillator (FRO) for generating an LO signal
Implementation Method 2
an output of the DDS is used to modulate the LO signal
Implementation Method 3
employing a quadrature up-conversion mixer to suppress unwanted sidebands
Data Source
Figure 1
Figure 2
Figure 3a~3c
AI summary
A signal generation system suitable for use in a radar system comprises a local oscillator (LO) and an intermediate frequency IF oscillator, wherein the IF oscillator is a Direct Digital Synthesiser, and the LO is a free running oscillator not itself locked to another oscillator but which acts as a clock reference for the DDS and is the highest frequency oscillator in the system. The LO may also act as a reference for a receive chain digitiser. The invention exploits phase noise advantages of a free running oscillator at some distance from the carrier whilst maintaining coherency with other system components. The system typically finds application in FMCW radars.