Maritime Surveillance Radar with Dynamic Aperture Synthesis
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Solution Overview
Problem
Current radar devices for maritime surveillance struggle to reconcile decametric spatial resolution with large swath width, essential for detecting small targets over vast ocean areas, due to conflicting requirements for repetition frequency and antenna design.
Innovation Solution
A synthetic partial aperture radar device with a low repetition frequency and means for coherent and incoherent image integration, achieving a swath width of approximately 1000 km and spatial resolution of a few tens of meters, combined with dynamic aperture beam orientation for enhanced reception gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high repetition frequency is used to achieve decametric spatial resolution, then the spatial resolution is improved, but the swath width is reduced
Solution Approach 1:
The patent applies dynamic aperture synthesis, where the antenna beam is dynamically steered and focused along the satellite's flight path to synthesize a larger effective aperture. This dynamic approach allows the system to achieve high spatial resolution (decametric) while maintaining a large swath width (approximately 1000 km) by effectively utilizing the satellite's motion to create a time-varying antenna pattern that integrates multiple observations.
Solution Approach 2:
The patent transitions from a static aperture approach to a dynamic temporal-spatial integration approach. By integrating signals over time as the satellite moves along its orbit, the system effectively adds the time dimension to the spatial aperture, creating a synthetic aperture that is much larger than the physical antenna. This allows simultaneous achievement of high resolution and wide coverage.
2Area of stationary object
If a low repetition frequency is used to increase swath width, then the radar coverage is improved, but the spatial resolution deteriorates
Solution Approach 1:
The patent uses dynamic beam steering and time-varying aperture synthesis to compensate for the low repetition frequency. By continuously adjusting the beam direction and integrating signals over the satellite's motion, the system recovers the spatial resolution that would otherwise be lost due to the low pulse repetition rate, achieving both wide swath and decametric resolution.
Solution Approach 2:
The patent implements continuous signal integration over the entire satellite pass, accumulating useful radar returns throughout the observation period. This continuous integration process maintains high spatial resolution despite the low repetition frequency by coherently combining multiple low-rate observations into a high-resolution image through the synthetic aperture effect.
3Measurement precision
If the repetition frequency is increased to improve spatial resolution, then the resolution is improved, but the number of ambiguous echoes increases
Solution Approach 1:
The patent employs dynamic aperture synthesis with time-varying beam steering that naturally suppresses ambiguous echoes. The dynamic focusing along the flight path creates a time-dependent point spread function that concentrates energy from true targets while dispersing ambiguous returns, effectively reducing ambiguity levels without requiring high repetition frequency.
Solution Approach 2:
The patent converts the potentially harmful effect of low repetition frequency (which would normally increase ambiguities) into a benefit by using the extended observation time to perform coherent integration. The low repetition rate allows longer integration periods, and the dynamic aperture synthesis processes this extended data to both suppress ambiguities and enhance resolution simultaneously.
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 configuration significantly improves the probability of detecting small targets by increasing the contrast between target and sea clutter signals, allowing for high-quality maritime surveillance over extensive areas.
Implementation Method 1
a radar which emits pulses at a certain frequency, called the repetition frequency, via a transmitting antenna, for example towards the ground, and measure then the echo returned by the ground to a receiving antenna of said radar
Implementation Method 2
the signal sent back to the radar by the objects illuminated by a pulse emitted by said radar
Implementation Method 3
The echo of a given target is characterized by its instant of reception and by its Doppler frequency resulting from the movement of the satellite
Data Source
Figure 1
AI summary
The present invention relates to a radar device for maritime surveillance, intended to be mounted on a platform moving at very high altitude, generally on a satellite. More specifically, the invention consists of a low-repetition-frequency partial aperture synthetic radar device, enabling high-quality maritime surveillance and ensuring good performance in terms of target detection probability and the ability to process large areas of the sea.