Active Radar Beacons for VTOL Landing in GNSS-Denied Conditions
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Solution Overview
Problem
Conventional radar altimeters for VTOL aircraft navigation in GNSS-denied conditions provide only vertical position information, and the use of passive radar reflectors is challenging due to difficulties in distinguishing between targets at the same range and the complexity of reflector placement, which affects navigation accuracy and integrity.
Innovation Solution
Implementing active radar beacons around a landing site that produce unique patterns of artificial echoes, allowing a radar sensor unit onboard the aircraft to determine horizontal and vertical positions through multilateration, even in GNSS-denied environments, by identifying and associating these patterns with stored beacon patterns in a database.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If passive radar reflectors are used to extend radar altimeter capabilities, then horizontal position information can be obtained, but the system complexity and installation difficulty increase significantly
Solution Approach 1:
Instead of using passive reflectors that require complex installation and distinction algorithms, the patent inverts the approach by using active radar beacons that actively transmit signals. This inversion simplifies the system by eliminating the need for complex reflector placement and makes target distinction straightforward through signal source identification.
Solution Approach 2:
The active radar beacons are self-contained units that generate their own radar signals and transmit them actively. This self-service capability eliminates the need for complex external installation infrastructure and simplifies the overall system architecture compared to passive reflectors that require careful placement and external coordination.
2Measurement precision
If passive radar reflectors are used, then navigation capability is enhanced, but the ability to distinguish between targets at the same range deteriorates due to sidelobes and wide antenna beamwidth
Solution Approach 1:
The patent inverts the passive detection approach by using active beacons that transmit known signals. This allows the receiving radar to clearly identify and distinguish between multiple targets at the same range by recognizing the unique signal sources, eliminating the ambiguity caused by sidelobes and wide beamwidth issues in passive systems.
3Area of stationary object
If radar reflectors are installed close to the helipad center to account for radar beamwidth, then measurement coverage is improved, but installation time and complexity increase
Solution Approach 1:
Active radar beacons are self-contained units that can be independently deployed without requiring precise coordination or complex installation procedures. This self-service nature significantly reduces installation time and complexity while maintaining adequate measurement coverage through their active signal transmission 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 enhances navigation accuracy and integrity by providing additional sources of horizontal and vertical position information, supporting all-weather operations and multiple landing pads without the need for additional onboard sensors, and ensures reliable 3D position estimation.
Implementation Method 1
transmitting radar signals from the radar sensor unit to an area around the landing site; receiving return signals in the radar sensor unit from the area around the landing site, the return signals including ground reflected signals
Implementation Method 2
Each active radar beacon produces a pattern of one or more artificial echoes; receiving return signals in the radar sensor unit from the area around the landing site, the return signals including ground reflected signals, and transmitted signals from the one or more active radar beacons
Data Source
AI summary
A method includes providing a radar sensor onboard a vehicle, and one or more active radar beacons around a landing site. Each beacon produces a pattern of one or more artificial echoes that is different from a pattern of echoes produced by others of the beacons. The method further includes guiding the vehicle toward the landing site by transmitting radar signals from the radar sensor to an area around the landing site; receiving return signals from the area around the landing site, including ground reflected signals and transmitted signals from each beacon; and determining whether artificial echoes are detected in the received return signals. When artificial echoes are detected, beacon parameters are loaded from an onboard active beacons database; patterns in the artificial echoes are identified and associated with corresponding beacons from the database; and a slant range to each of the beacons is estimated through the patterns.