Single-Antenna FMCW Radar Delay Matching for Phase Noise Cancellation
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Solution Overview
Problem
Frequency modulated continuous wave (FMCW) radar systems that transmit and receive from a single antenna face challenges in signal isolation, leading to increased noise and reduced sensitivity due to signal coupling, which is critical in high-precision applications like radar altimeters where sensitivity is crucial.
Innovation Solution
The implementation of a circulator to provide isolation between the transmit and receive paths, combined with a delay match path using a local oscillator reference signal to cancel phase noise from reflected and leakage signals, and the selection of an antenna with low reflection levels and flat group delay characteristics to minimize noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a single antenna is used for both transmitting and receiving, then the size of the radar is reduced, but the isolation between transmit and receive path decreases resulting in increased signal coupling and reduced sensitivity
Solution Approach 1:
A circulator is introduced as an intermediary component between the single antenna and the transmit/receive paths. The circulator enables the single antenna to be shared while providing isolation between transmit and receive modes, thus maintaining radar sensitivity without requiring multiple antennas.
Solution Approach 2:
A reflected power canceller is implemented to preemptively counteract the signal coupling and noise interference that would otherwise occur. The canceller generates an opposing signal that cancels out the leaked transmit signal before it can interfere with the receive path, preserving measurement precision.
2Power
If transmit power is increased to improve signal strength, then the radar can detect weaker signals, but the leaked transmit signal becomes stronger and drowns out the receive signal entirely
Solution Approach 1:
The reflected power canceller captures the harmful leaked transmit signal and converts it into a beneficial cancellation signal. By sampling the transmit path and adjusting phase and amplitude, the system transforms the harmful leakage into a counter-signal that actively reduces the interference, allowing high transmit power to be used without sacrificing receive sensitivity.
3Measurement precision
If separate antennas are used for transmitting and receiving, then isolation between transmit and receive path is improved, but the size of the radar increases to accommodate each antenna and spacing between them
Solution Approach 1:
The single antenna is designed to perform multiple functions - both transmitting and receiving - eliminating the need for separate antennas. The circulator and reflected power canceller enable this multi-functionality while maintaining the isolation that would normally require separate antennas, thus reducing radar size without sacrificing signal isolation.
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 enhances the sensitivity of the FMCW radar by effectively canceling phase noise and reducing signal coupling, ensuring accurate measurements and improved performance in high-precision applications such as radar altimeters.
Implementation Method 1
The implementation of a circulator to provide isolation between the transmit and receive paths
Implementation Method 2
a delay match path using a local oscillator reference signal to cancel phase noise from reflected and leakage signals
Implementation Method 3
the propagation time of the local oscillator reference signal from the coupler to the mixer through the delay path is the same as the propagation time of a reflected signal
Implementation Method 4
sensing reflections of the transmit signal; an antenna with low reflection levels and flat group delay characteristics
Data Source
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AI summary
One embodiment is directed towards a FMCW radar having a single antenna. The radar includes a transmit path having a voltage controlled oscillator controlled by a phase-locked loop, and the phase-locked loop includes a fractional-n synthesizer configured to implement a FMCW ramp waveform that ramps from a starting frequency to an ending frequency and upon reaching the ending frequency returns to the starting frequency to ramp again. The radar also includes a delay path coupled between a coupler on the transmit path and a mixer in a receive path. The delay path is configured to delay a local oscillator reference signal from the transmit path such that the propagation time of the local oscillator reference signal from the coupler to the mixer through the delay path is between the propagation time of signal reflected off the antenna and the propagation time of a leakage signal through a circulator.