Coherence Switching for Distributed Aperture Imaging Gain Stability
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Solution Overview
Problem
Distributed aperture imaging systems face challenges in compensating for amplifier gain fluctuations, particularly in millimeter and submillimeter wavelength bands, where larger apertures are required, leading to increased size, weight, and complexity, and existing solutions like Dicke-type systems further exacerbate these issues.
Innovation Solution
The system employs coherence switching by scrambling the phases of detector channels and local oscillator phases in a distributed aperture imaging system, allowing for phase-locked and phase-scrambled states, enabling compensation for temporal gain variations through image subtraction and processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If distributed aperture imaging is used to achieve desired resolution in millimeter and submillimeter bands, then aperture size is increased, but system volume and weight increase
Solution Approach 1:
The imaging system divides the aperture into multiple distributed detector elements (N detectors) spaced apart, rather than using a single continuous large aperture. Each detector captures a portion of the scene, and the signals are combined through correlation processing to achieve the resolution of a full-aperture system with much reduced weight and volume.
2Reliability
If Dicke-type switching is used to compensate for amplifier gain fluctuations, then gain stability is improved, but device complexity and insertion losses increase
Solution Approach 1:
The system uses a feedback mechanism where the output of each detector is correlated with the output of a reference detector. This correlation process provides automatic compensation for temporal gain variations in the low-noise amplifiers, eliminating the need for complex external Dicke switching mechanisms while maintaining gain stability.
Solution Approach 2:
A reference detector serves as an intermediary element that captures the same scene as the other detectors. By correlating the signals from multiple detectors with the reference detector signal, the system indirectly measures and compensates for amplifier gain fluctuations without requiring direct switching to a separate reference source.
Data Source
AI summary
A first image may be obtained using locked (relative) phases. A second image may be obtained using unlocked (e.g., randomized) phases. Data of the second image may be subtracted from data of the first image. The result may then undergo further processing, if desired, e.g., to further enhance the resulting image.