Interferometric Time Delay of Arrival for Angle of Arrival
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Solution Overview
Problem
Existing direction finding systems face challenges in achieving precise and unambiguous angles of arrival (AoA) measurements for RF signals, especially for frequency agile emitters and wide frequency coverage, due to the periodic nature of phase differences and limited precision with antenna spacings greater than one-half wavelength.
Innovation Solution
The method combines phase interferometry (PI) and time difference of arrival (TDOA) techniques to iteratively refine AoA estimates by averaging signal component measurements, reducing ambiguity and error bounds, and recalculating PI estimates for multiple signal components, allowing for precise AoA determination even with widely spaced antennas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If antenna elements are spaced more than one-half wavelength apart, then measurement precision is improved, but multiple ambiguous angles of arrival are computed due to periodic nature of phase difference
Solution Approach 1:
The patent uses TDOA as an intermediary to resolve the ambiguity in PI measurements. The coarse TDOA estimate serves as a mediator that identifies which of the multiple PI ambiguity solutions is the correct AoA, thereby eliminating the information loss caused by periodic phase differences.
Solution Approach 2:
The patent combines two direction finding techniques - Phase Interferometry (PI) and Time Difference of Arrival (TDOA) - into a hybrid system. The high-precision PI measurements are merged with the unambiguous but lower-precision TDOA measurements to achieve both precision and unambiguity in AoA determination.
2Adaptability or versatility
If antenna spacing is increased to provide coverage at all azimuths, then adaptability is improved, but measurement precision deteriorates for frequency agile emitters
Solution Approach 1:
The patent creates a universal direction finding system that works across multiple frequencies and for both frequency-stable and frequency-agile emitters. The hybrid PI-TDOA approach provides multi-functionality, enabling the same antenna configuration to achieve precise AoA measurements regardless of emitter frequency behavior.
3Adaptability or versatility
If a single baseline interferometer is used for wide frequency coverage, then adaptability is improved, but unambiguous high precision AoA measurements cannot be achieved
Solution Approach 1:
The patent changes the operational parameters of the interferometer by dynamically adjusting the effective baseline or processing approach based on frequency. This allows the system to maintain unambiguous precise measurements across a wide frequency range without requiring multiple physical antenna configurations.
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 enables precise and unambiguous AoA measurements across a broad range of frequencies, including for frequency agile emitters, with improved accuracy and reduced ambiguity, suitable for existing antenna systems on aircraft.
Implementation Method 1
receiving at a processor corresponding first and second components of a first signal detected at first and second antenna elements of the antenna pair
Implementation Method 2
determining one or more features of the received signal, including a phase difference between corresponding phases of the first and second signal components
Implementation Method 3
a time difference of arrival (TDOA) between the signal components arriving at the first and second antenna elements
Data Source
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AI summary
Systems and methods for determining an angle of arrival (AoA) of a signal received from an emitters at a pair of antennas (220) spaced apart by more than one half wavelength of the received signal (210). Features of the signal are determined, including a phase difference between signal components detected at the antennas (245), and a time difference of arrival (TDOA) (250) having a known measurement error. A set of TDOA possibilities bounded by the known TDOA measurement error and a set of AoA estimates using phase interferometry (PI) within the range are calculated. The TDOA set is iteratively reduced to determine a precise AoA estimate for the emitter.