SAR Phase Center Shifting for Equidistant Sampling
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Solution Overview
Problem
Synthetic aperture radar systems face limitations in imaging large areas while maintaining high geometric resolution due to the need for precise tuning of speed, size, and number of receiving apertures or antennas, and pulse repetition frequency, leading to non-equidistant sampling that degrades radar image quality.
Innovation Solution
A novel approach that allows flexible adjustment of the transmitting antenna's phase center during recording, enabling compensation for deviations in equidistant sampling by continuously shifting the electrically effective center of the transmitting antenna, thereby relaxing the strict conditions on speed, size, and number of SAR sensor elements and pulse repetition frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pulse repetition frequency is adjusted to match the speed and size of receiving apertures, then equidistant sampling is achieved, but the system loses flexibility in operating conditions and imaging large areas
Solution Approach 1:
The transmitting antenna system dynamically shifts its phase center position between different azimuth locations during data acquisition. This dynamic adjustment allows the system to compensate for non-equidistant sampling caused by varying pulse repetition frequencies, maintaining sampling quality while enabling flexible operation for imaging large areas
Solution Approach 2:
The system changes the phase center position parameter of the transmitting antenna based on the actual pulse repetition frequency and platform speed. By adjusting this parameter, the system adapts to different operating conditions and maintains equidistant sampling without being constrained to a single optimal PRF
2Ease of operation
If the phase center of the transmitting antenna is fixed, then the system is simple to operate, but non-equidistant sampling degrades image quality
Solution Approach 1:
Rather than fixing the phase center, the system dynamically adjusts the phase center position according to the actual operating conditions (platform speed and pulse repetition frequency). This dynamic approach maintains image quality by ensuring equidistant sampling while automatically adapting to different operational scenarios
Solution Approach 2:
The system uses feedback from the actual platform speed and pulse repetition frequency measurements to determine the appropriate phase center position. This closed-loop control ensures that the phase center is optimally positioned to achieve equidistant sampling under current operating conditions
3Area of stationary object
If multiple receiving apertures are used to image large areas, then coverage area increases, but the sampling becomes non-equidistant when PRF is not optimally tuned
Solution Approach 1:
The transmitting antenna system dynamically shifts its phase center to compensate for the non-equidistant sampling that occurs when using multiple receiving apertures with non-optimal PRF. This dynamic adjustment restores sampling equidistance across the extended imaging area
Solution Approach 2:
The system introduces an additional degree of freedom by adjusting the phase center position in the azimuth direction. This extra dimensional control allows compensation for sampling errors introduced by using multiple receiving apertures, maintaining sampling quality across larger areas
Data Source
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AI summary
A continually adapted pulse-to-pulse shift of the electrically effective phase center on the side of the transmitting antenna (Tx; Tx1, Tx2, Tx3) in the azimuth direction in connection with the SAR antenna control of a multi-aperture SAR system is designed such that, in the case of an existing pulse repetition frequency (PRF) due to the likewise shifted position of the effective phase center of the entire antenna (Tx; Tx1, Tx2, Tx3; Rx; Rx1, Rx2, Rx3), a compensation or complete correction of non-equidistant scanning in the azimuth direction is achieved. The principle of the pulse-to-pulse shift of the position of the effective phase center of the antenna for achieving the best possible equidistant scanning can be expanded to the side of the receiving antenna (Rx; Rx1, Rx2, Rx3) and to multi-aperture antennas. The method according to the invention can be advantageously combined with a subsequent digital beam formation on the receiving antenna side. Use with SAR earth remote sensing.