HF Direction of Arrival Measurement Using Cross-Loop Antenna Calibration
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Solution Overview
Problem
Existing methods for determining the direction of arrival of high-frequency electromagnetic waves from a platform of limited size are prone to errors due to parasitic reflections and spurious couplings, especially when detecting signals with non-zero elevation angles or vertical polarization, and lack a reliable quality assessment for bearing angle measurements.
Innovation Solution
A method using a cross-loop antenna or Adcock-type antenna array that involves a calibration phase to record intercorrelation vectors, which are then correlated with measurement phase signals to determine the direction of arrival, accounting for the electromagnetic environment and reducing noise influence through averaging and normalization, and providing a quality score for bearing angle measurements based on correlation levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a large antenna is used to determine the direction of arrival of HF signals, then measurement precision is improved, but device complexity and platform size requirements worsen
Solution Approach 1:
The patent applies preliminary action by performing a calibration phase before actual measurements. During calibration, the antenna system characterizes its response to signals from known directions and stores this information in a lookup table. This pre-characterization allows the system to compensate for geometric constraints and environmental factors during actual operation, achieving accurate bearing measurements without requiring a large physical antenna array.
2Device complexity
If conventional Watson-Watt algorithm is used with limited-size antenna, then device complexity is reduced, but measurement precision deteriorates due to parasitic reflections and spurious couplings
Solution Approach 1:
The patent converts the harmful effects of parasitic reflections and spurious couplings into beneficial calibration data. By deliberately measuring the antenna system's response to signals from known directions during calibration, the system captures the complete electromagnetic environment including all parasitic effects. This calibrated information is then used to correct subsequent measurements, transforming what would be sources of error into factors that improve measurement accuracy in the operational environment.
Solution Approach 2:
The patent creates a computational model (lookup table) that copies and stores the antenna system's characteristic response under various conditions. Instead of physically eliminating parasitic effects or using complex correction models, the system measures and stores the actual response characteristics during calibration, then uses this copied information to determine bearing angles during operation. This approach accurately represents the real-world behavior of the antenna system without requiring complex theoretical corrections.
3Use of energy by moving object
If signals from multiple directions including non-zero elevation angles are received, then signal strength is improved, but measurement precision deteriorates due to erroneous bearing values
Solution Approach 1:
The patent applies local quality by creating direction-specific calibration data for different spatial regions. The calibration process measures the antenna response to signals arriving from specific bearing angles and elevation angles separately, storing these characteristics in the lookup table. During operation, the system uses the calibration data corresponding to the specific direction of the received signal, ensuring that the bearing determination is based on the appropriate directional characteristics and not contaminated by responses from other directions.
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 method effectively reduces the impact of parasitic reflections and spurious couplings, providing accurate and reliable direction-of-arrival measurements by naturally accounting for the antenna's environment and distinguishing between reliable and erroneous measurements.
Implementation Method 1
a cross-loop antenna or an antenna array of Adcock type, which comprises at least the following steps: during a preparatory calibration phase, acquire and record the measurements by the antenna of a calibration signal
Implementation Method 2
for each channel of frequency f i, correlate the signals acquired with the recordings resulting from the frequency calibration close to f i and determine the direction of arrival of the signals by looking for the bearing angle θ for which the maximum correlation is reached
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 3~6
AI summary
The present invention relates to a method of measuring the direction of arrival in terms of bearing ? of HF-band radioelectric signals received by a cross-frame antenna. The method comprises at least the following steps: ° during a calibration phase (101), acquiring and recording the measurements by the antenna of a calibration signal varying in frequency and in angle of bearing; during a measurement phase (102) during which the angle or angles of bearing of arrival of signals detected by the antenna is or are determined, acquiring the signals detected on at least one frequency channel, then, for each frequency channel fi, correlating the signals acquired with the recordings of frequency close to fi which emanate from the calibration and determining the direction of arrival of the signals by searching for the angle of bearing ? for which the maximum correlation is achieved.