FMCW Radar Altimeter Phase Refinement for Precision
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Solution Overview
Problem
Conventional FMCW radar altimeters have limited range resolution, typically offering 3 ft of resolution due to their 200 MHz operating bandwidth, which is insufficient for precise altitude measurements, especially when the target is close to the aircraft.
Innovation Solution
The method involves transmitting a radar signal at a first frequency, ramping the frequency to a second frequency, and processing reflections to determine an approximate distance based on the phase difference between the phases of reflections received at both frequencies, allowing for refined distance measurements by using fixed frequency transmissions when the target is close, thereby improving resolution to less than 3 ft.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional FMCW radar operates with 200 MHz bandwidth, then the system is simple to operate, but the range resolution is limited to around 3 ft
Solution Approach 1:
The measurement process is segmented into two distinct phases: a frequency ramp phase for coarse range measurement and fixed frequency phases for fine range refinement. This segmentation allows the system to achieve high resolution without continuously operating at full bandwidth, thereby managing complexity while improving measurement precision.
Solution Approach 2:
The radar system dynamically switches between different operating modes - transitioning from frequency ramp transmission to fixed frequency transmission based on the detected target range. This dynamic adaptation enables the system to optimize resolution for close targets while maintaining operational simplicity for farther targets.
2Measurement precision
If the radar uses frequency ramp for distance measurement, then the measurement process is simple, but the resolution is insufficient for close targets
Solution Approach 1:
The system performs a preliminary distance measurement using the frequency ramp to determine the approximate target range. Based on this preliminary measurement, it decides whether to initiate the more time-consuming fixed frequency refinement phase. This preliminary action filters out targets that don't require high-resolution measurement, preserving measurement speed while improving resolution when needed.
Solution Approach 2:
The system uses feedback from the coarse range measurement to control the subsequent measurement strategy. When the preliminary measurement indicates a close target, the system activates the fixed frequency refinement mode. This feedback mechanism ensures that high-resolution measurement is applied selectively, balancing precision requirements with measurement efficiency.
3Measurement precision
If fixed frequency transmissions are added for refinement, then resolution improves to less than 3 ft, but the operation becomes more complex
Solution Approach 1:
The radar system automatically determines when high-resolution measurement is needed based on its own preliminary measurements. The system self-manages the complexity by autonomously switching between measurement modes without requiring external intervention or complex user configuration, thereby maintaining ease of operation while achieving improved resolution.
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 range resolution of FMCW radar altimeters, enabling more precise altitude measurements, particularly when the target is near, by refining the distance calculation using phase differences, thus addressing the limitations of conventional systems.
Implementation Method 1
receiving reflections of the radar signal
Implementation Method 2
determining an approximate distance to a target from which the reflections are received based on an amount of time between transmission of the radar signal having the frequency ramp and reception of a reflection of the radar signal having the frequency ramp
Implementation Method 3
A first phase of a reflection of the radar signal transmitted at the first frequency can be determined, wherein the first phase is the phase of the radar signal as received. A second phase of a reflection of the radar signal transmitted at the second frequency can also be determined, wherein the second phase is the phase of the radar signal as received. A phase difference between the first phase and the second phase can be determined and the approximate distance to the target can be refined based on the phase difference between the first phase and the second phase.
Data Source
AI summary
One embodiment is directed to a method for operating a radar altimeter. The method includes transmitting a radar signal at a first frequency, ramping the frequency of the radar signal from the first frequency to a second frequency, and transmitting the radar signal at the second frequency. The reflections can be processed by determining an approximate distance to a target based reflections of the frequency ramp and the approximate distance can be refined based on a phase difference between a reflection of the radar signal transmitted at the first frequency and a reflection of the radar signal transmitted at the second frequency.