Dual Directional Coupler Layout for Low-Loss RF Amplifier Feedback
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Solution Overview
Problem
Existing radio frequency power amplifier systems for magnetic resonance imaging require multiple high-power directional couplers, leading to increased complexity and cost, while also reducing the signal-to-noise ratio due to the need for large attenuators.
Innovation Solution
A multi-port directional coupler with six ports is introduced, which replaces two high-power directional couplers by incorporating additional ports for improved directivity and signal-to-noise ratio, and is used in conjunction with a low-power directional coupler to form a dual directional coupler system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a dual directional coupler with large attenuator is used to sample output signals, then the power of coupled signals is reduced to milliwatts for control processing, but the signal-to-noise ratio is significantly reduced, especially for low-power sideband inputs
Solution Approach 1:
The patent divides the single dual directional coupler into two separate directional couplers: a first directional coupler for power amplification output and a second directional coupler for signal sampling. This segmentation allows the first coupler to handle high-power signals while the second coupler processes low-power sampled signals, thereby preserving signal-to-noise ratio while achieving the required power reduction for control processing.
Solution Approach 2:
The patent introduces an intermediary signal path where the output of the first directional coupler is coupled to the input of the second directional coupler. This intermediary arrangement allows the sampled signal to be transferred from the high-power domain to the low-power control domain with minimal noise introduction, as the second coupler is specifically designed for low-power signal handling.
2Reliability
If two high-power directional couplers are added for output monitoring and matching detection, then the monitoring and protection functions are improved, but the cost and device complexity are increased
Solution Approach 1:
The patent makes the first directional coupler serve multiple functions: it provides power amplification output coupling and simultaneously enables output power monitoring and antenna matching detection through its coupled and isolated ports. This multi-functionality eliminates the need for separate high-power directional couplers dedicated solely to monitoring, thereby reducing device complexity while maintaining reliability.
Solution Approach 2:
The patent combines the power amplification function and the monitoring function into a single first directional coupler structure. The coupled port provides power amplification output while the isolated port simultaneously monitors output power and antenna matching conditions, merging multiple functions into one component to reduce overall system complexity.
3Loss of information
If the coupled port output is directly connected to the control part, then the signal-to-noise ratio is maintained, but the power is too high for the control processing board
Solution Approach 1:
The patent segments the signal processing into two distinct stages handled by separate directional couplers. The first directional coupler handles high-power signals for power amplification, while the second directional coupler handles low-power sampled signals for control processing. This segmentation allows the control board to receive appropriately powered signals while maintaining signal-to-noise ratio through the second coupler's low-power operation.
Solution Approach 2:
The second directional coupler acts as an intermediary between the high-power first directional coupler and the low-power control processing board. It transfers the sampled signal from the high-power domain to the low-power domain with minimal noise introduction, enabling the control board to process the signal at appropriate power levels while preserving signal-to-noise ratio.
Data Source
AI summary
The invention relates to a directional coupler, coupling high power and low power is used to replace existing two high-power directional couplers, thus reducing the cost and reducing the insertion loss of high-power radio frequency channels. The directional coupler cooperates with a control conditioning board, a splitter, a multi-path radio frequency power amplifier and a combiner to form the radio frequency power amplifier system, and the system is connected to a spectrometer; on one hand, by using a standard signal output by the spectrometer and a feedback signal of the directional coupler, nonlinearity caused by the power amplifier is corrected to achieve magnet-free linear radio frequency power amplification and anomaly protection; and on the other hand, the spectrometer can be used for monitoring the output power of the directional coupler and monitoring antenna matching, so as to provide dual protection for the radio frequency power amplifier system.