RF Power Amplifier Measurement Using Complex Scattering Parameters
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Solution Overview
Problem
Current power measurement methods in magnetic resonance imaging (MRI) systems are uncertain due to their reliance on the directivity of directional couplers, which can lead to measurement inaccuracies, especially with high reflection in the transmission chain, and compromise power handling capabilities.
Innovation Solution
A transmit/receive RF system that uses a coupling device to detect both amplitude and phase information of coupled signals, allowing for the calculation of operational parameters of the RF power amplifier as complex-valued functions of complex scattering parameters, reducing dependency on directional coupler directivity and enabling more accurate power measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If directional couplers with high directivity are used for power measurement, then measurement precision is improved, but power handling capability deteriorates and air breakdown risk increases
Solution Approach 1:
The patent changes the measurement approach from scalar to vector method, utilizing complex scattering parameters (S-parameters) that capture both magnitude and phase information. This parameter transformation allows accurate power measurement without requiring high directivity couplers, thereby maintaining power handling capability while improving measurement accuracy
Solution Approach 2:
The patent replaces the traditional scalar measurement system with a vector measurement system that uses complex scattering parameters. This substitution enables the use of couplers with lower directivity specifications while achieving superior measurement accuracy through mathematical processing of complex signal components
2Measurement precision
If directional couplers with high directivity are used for power measurement, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent replaces complex high-directivity directional couplers with simpler couplers by substituting the measurement methodology. The vector method using complex scattering parameters achieves high measurement precision through signal processing rather than through complex hardware design, thereby reducing overall device complexity
Solution Approach 2:
By transforming the measurement from scalar to vector domain using complex S-parameters, the patent achieves high measurement precision without requiring complex coupler designs. The complexity is shifted from hardware specifications to mathematical processing, simplifying the physical measurement system
3Ease of operation
If scalar measurement method is used with directional couplers, then ease of operation is maintained, but measurement precision deteriorates due to dependency on directivity
Solution Approach 1:
The patent substitutes the scalar measurement method with a vector measurement method that uses complex scattering parameters. This replacement maintains operational simplicity through automated complex signal processing while dramatically improving measurement precision by eliminating directivity dependency
Solution Approach 2:
The patent introduces complex scattering parameters as an intermediary that mediates between the simple coupler output and the precise power measurement requirement. The complex S-parameters capture both magnitude and phase information, enabling accurate power measurement without directivity constraints while keeping the measurement system easy to operate
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 provides more accurate and real-time measurement of RF power, improving safety and regulatory compliance by reducing measurement uncertainty and allowing for the use of coupling devices with higher power handling capabilities and lower directivity requirements.
Implementation Method 1
a coupling device coupled between the RF power amplifier and the RF antenna and configured to couple out a fraction of a reflected power flowing from the RF antenna toward the RF power amplifier and a fraction of a forward power flowing from the RF power amplifier toward the RF antenna
Implementation Method 2
a wave detector coupled to the coupling device and configured to detect amplitude and phase information of the first coupled signal and the second coupled signal
Implementation Method 3
an RF power amplifier configured to supply electrical RF power to the RF antenna
Data Source
AI summary
A transmit/receive RF system for a magnetic resonance examination system is described. The transmit/receive RF system comprises an RF antenna, an RF power amplifier configured to supply electrical RF power to the RF antenna, a coupling device coupled between the RF power amplifier and the RF antenna and configured to couple out fractions of a reflected power flowing from the RF antenna toward the RF power amplifier and a forward power flowing from the RF power amplifier toward the RF antenna to output a first coupled signal VREV and a second coupled signal VFWD, a wave detector coupled to the coupling device and configured to detect amplitude and phase information of the first coupled signal VREV and the second coupled signal VFWD, and a parameter calculator coupled to the wave detector and configured to calculate an operational parameter of the RF power amplifier based on complex scattering parameters of the coupling device and the detected amplitude and phase information of the first coupled signal VREV and second coupled signal VFWD.