Impedance Measurement Using S-Parameters to Stabilize Sensitivity
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Solution Overview
Problem
Conventional impedance measurement methods are limited to frequencies below 3 GHz, and existing apparatuses struggle to provide accurate measurements across a wide range of impedances, especially when the impedance is far from the characteristic impedance, leading to reduced measurement sensitivity and increased error magnification.
Innovation Solution
The method involves connecting a device under test (DUT) in series or parallel to a signal line, using a network analyzer to measure S-parameters S11 and S21, and calculating impedance Zx using formulas that stabilize measurement sensitivity across all ranges, while canceling out apparatus drift by combining forward and reverse direction measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional balanced bridge methods are used for impedance measurement, then measurement accuracy is maintained, but frequency range is limited to no more than approximately 110 MHz
Solution Approach 1:
The patent changes the measurement parameters by transitioning from traditional balanced bridge methods to S-parameter based measurement methods. By measuring S11 (reflection coefficient) and S21 (transmission coefficient) and using mathematical transformations, the system achieves accurate impedance measurement across extended frequency ranges up to approximately 3 GHz and beyond, resolving the frequency range limitation while maintaining measurement accuracy.
2Speed
If RF I-V methods are used for impedance measurement, then frequency range is extended to approximately 1 MHz to 3 GHz, but measurement accuracy deteriorates for wide range of impedances
Solution Approach 1:
The patent introduces S-parameters (S11 and S21) as intermediary measurement quantities that bridge the gap between direct RF I-V measurements and accurate impedance determination. By measuring reflection and transmission coefficients and applying mathematical transformations, the system recovers accurate impedance values across wide impedance ranges while maintaining the extended frequency capability of RF methods.
3Ease of operation
If reflection coefficient method is used, then impedance measurement is simplified, but measurement sensitivity decreases when impedance is far from characteristic impedance
Solution Approach 1:
The patent merges the measurement of both S11 (reflection coefficient) and S21 (transmission coefficient) to compensate for the sensitivity limitations of using S11 alone. By combining these two measurement parameters and applying appropriate mathematical transformations, the system maintains high measurement sensitivity across the entire impedance range while preserving the operational simplicity of S-parameter based measurement.
4Adaptability or versatility
If transmission method is used, then measurement range is extended, but error magnification increases when impedance is far from characteristic impedance
Solution Approach 1:
The patent employs mathematical feedback mechanisms through the use of transformation formulas that process S11 and S21 measurements. These transformations effectively compensate for error magnification effects by using the relationship between reflection and transmission coefficients to correct measurements, thereby maintaining high precision across extended measurement ranges and impedances far from characteristic impedance.
Data Source
AI summary
An impedance measurement method is provided having a certain level of measurement sensitivity across all ranges of impedance and capable of covering a wide measurement range. In the method, a device under test (DUT) is connected in series or in parallel to a signal line, a measurement signal is transmitted from a signal source, an input signal a1 into the DUT, a reflected signal reflected from the DUT, and a passed signal that passed through the DUT are measured, S-parameters S11 and S21 are calculated based on respective measured values of the input signal, the reflected signal, and the passed signal, and an impedance Zx of the DUT is calculated based on a formula: Zx=2Z0S11/S21, where Z0 is a characteristic impedance.