Stepped-Frequency Target Imaging with Modulated Bandwidth Expansion
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Solution Overview
Problem
Current sensing technologies using linearly swept sources face challenges such as nonlinearity issues that degrade range resolution, require additional hardware for correction, and are limited by high manufacturing costs for ideal swept sources with high bandwidth.
Innovation Solution
The implementation of a stepped frequency swept source with modulation to increase bandwidth without excessive cost, using a modulated stepped frequency waveform that spreads constant frequencies across the entire bandwidth, allowing image reconstruction through interference with an unmodulated stepped frequency waveform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a linearly swept source is used for sensing, then range estimation can be performed, but range resolution degrades when the swept source is not completely linearly modulated due to nonlinearity
Solution Approach 1:
The patent uses a reference copy of the swept source signal to characterize and correct nonlinearity. By capturing a reference signal from a known reference mirror and comparing it with the actual swept source behavior, the system creates a digital model of the nonlinearity that can be compensated for in range estimation, eliminating the need for perfect hardware linearity.
Solution Approach 2:
The system implements feedback by using the reference signal to continuously characterize the swept source nonlinearity and apply corrections to the range estimation process. The reference measurement provides feedback information about the actual frequency-time relationship, which is then used to adjust subsequent measurements and maintain accurate range resolution despite nonlinearity.
2Measurement precision
If a dedicated reference path is added to correct nonlinearity, then non-linearity correction can be achieved, but hardware resources increase
Solution Approach 1:
The reference mirror serves multiple functions: it provides a known reflection point for range calibration, characterizes the swept source nonlinearity, and enables correction of range estimates. This single reference element performs what would otherwise require multiple separate calibration components, reducing overall hardware complexity while achieving non-linearity correction.
3Measurement precision
If high bandwidth swept sources are used to increase resolution, then image resolution improves, but manufacturing cost increases significantly
Solution Approach 1:
The system achieves high-resolution imaging by using multiple copies of lower-bandwidth frequency components that are swept across different frequency ranges. Instead of requiring a single expensive high-bandwidth source, the system synthesizes the equivalent information content using multiple affordable lower-bandwidth sources sweeping through different frequency segments, thereby reducing manufacturing cost while maintaining resolution.
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 approach enables high-bandwidth image reconstruction with reduced manufacturing costs and improved range resolution, overcoming the limitations of nonlinearity and hardware requirements in existing systems.
Implementation Method 1
a mixer to interfere the unmodulated stepped frequency waveform and the reflection of the modulated stepped frequency waveform to produce a beat signal of the interference of the unmodulated stepped frequency waveform with the reflection of the modulated stepped frequency waveform
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
A system for a target image reconstruction includes a stepped frequency transmitter configured to emit a stepped frequency waveform having different constant frequencies at different periods of time and a modulator configured to modulate the stepped frequency waveform emitted at each period of time with a modulation signal to output a modulated stepped frequency waveform with an increased bandwidth. The system includes a transceiver configured to transmit the modulated stepped frequency waveform to a target and to accept reflection of the modulated stepped frequency waveform reflected from the target, a mixer to interfere the unmodulated stepped frequency waveform and the reflection of the modulated stepped frequency waveform to produce a beat signal of the interference of the unmodulated stepped frequency waveform with the reflection of the modulated stepped frequency waveform, and a signal processor to reconstruct an image of the target from the beat signal.