Alternating-Beam SAR Swath Expansion With Variable PRF
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Solution Overview
Problem
Conventional synthetic aperture radar systems face limitations in achieving a large range swath due to the inherent limit on reception time between consecutive pulses, which is challenging for smaller antennas, especially when the antenna is not tall enough to form narrow enough beams to suppress ambiguous radar returns.
Innovation Solution
A synthetic aperture radar system with an elongate phased array antenna oriented in the elevation direction, using temporally alternating sets of receive beams and varying pulse repetition frequencies to form multiple swaths without Doppler ambiguity, allowing for wider swath coverage by overlapping subswaths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a conventional single feed scan mode radar system is used, then the system structure is simple, but the range swath coverage is limited by the reception time window between consecutive transmitted pulses
Solution Approach 1:
The radar system divides the coverage area into multiple swaths (first swath and second swath) and processes them separately using different pulse repetition frequencies. Each swath is further divided into subswaths that are received by different receive beams, allowing the system to overcome the limitation of single-receive-beam systems and achieve wider total coverage.
Solution Approach 2:
The system dynamically switches between different pulse repetition frequencies (first PRF for first swath, second PRF for second swath) and alternates between different sets of receive beams. This dynamic adaptation allows the system to optimize performance for different swath requirements and achieve continuous wide coverage without Doppler ambiguities.
2Weight of stationary object
If the antenna is made smaller, then the device weight and size are reduced, but the antenna cannot form narrow enough beams to suppress radar returns from ambiguous ranges
Solution Approach 1:
The system changes the pulse repetition frequency parameter between different swaths (first PRF and second PRF) to resolve range ambiguities. By using different PRFs for different swaths and interleaving their reception, the system can distinguish between ambiguous range returns without requiring a taller antenna to form narrower beams.
Solution Approach 2:
The controller acts as an intermediary that coordinates the alternating reception between first and second sets of receive beams at different PRFs. This intermediary function allows the system to process multiple swaths with different characteristics and combine them into a unified wide coverage image, compensating for the smaller antenna's limited beam narrowness.
3Productivity
If the pulse repetition frequency is increased, then the data collection rate is improved, but Doppler ambiguities occur within the antenna beam width
Solution Approach 1:
The system segments the data collection process into separate first and second swaths, each collected at a different pulse repetition frequency. By assigning different PRFs to different spatial segments (swaths), the system can increase overall data collection rate while maintaining reliable Doppler measurement within each segmented swath.
Solution Approach 2:
The system employs periodic alternating action between the first set of receive beams and the second set of receive beams. The controller alternates reception between these sets in a periodic manner, with each set operating at its own PRF. This periodic alternation allows the system to achieve high average data collection rates while each individual reception period maintains proper PRF for avoiding Doppler ambiguities.
Data Source
AI summary
A synthetic aperture radar (SAR) for a flight vehicle may include an elongate phased array antenna oriented with a long axis in an elevation direction. The elevation direction is normal to a direction of flight of the flight vehicle. A transmitter is coupled to the elongate phased array antenna, and a receiver is coupled to the elongate phased array antenna. A controller is coupled to the transmitter and receiver and is configured to generate temporally alternating sets of receive beams for respective swaths to be used to form a SAR image across a surface below the flight vehicle. The same center frequency is used to create consistent SARs for all swaths, allowing for coherent combination between subsequent passes over the same swath.