Mixed-Mode Scattering Matrix Measurement Using VNA
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Solution Overview
Problem
Current vector network analyzers (VNAs) face challenges in directly measuring mixed-mode scattering matrices of active devices with balanced ports, particularly due to non-ideal hybrid couplers and signal splitters, which limit frequency range and measurement accuracy.
Innovation Solution
A method that corrects system errors in unbalanced waves before calculating amplitude and phase changes for signal generators, allowing direct measurement of mixed-mode parameters without the need for auxiliary components like signal splitters, and accounts for coupling effects between signal branches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If hybrid couplers and signal splitters are used to generate differential and common-mode signals, then measurement capability for balanced ports is enabled, but measurement accuracy and frequency range are limited due to non-ideal components
Solution Approach 1:
The patent extracts and removes the hybrid coupler and signal splitter from the measurement system, replacing them with a method that uses only the VNA's existing unbalanced ports. By taking out these non-ideal components, the invention eliminates their limitations on measurement accuracy and frequency range while retaining the capability to measure balanced ports through mathematical conversion of S-parameters.
Solution Approach 2:
The invention makes the VNA universally applicable to both unbalanced and balanced ports without requiring different hardware configurations. By using the same unbalanced VNA ports for both measurement types and converting results mathematically, the system achieves multi-functionality without the limitations of dedicated balanced measurement hardware.
2Measurement precision
If hybrid circuits are used to generate pure opposite-mode and common-mode signals, then measurement accuracy improves, but the frequency range is limited to a ratio of approximately 1:8
Solution Approach 1:
The patent changes the measurement approach from hardware-based signal generation to mathematical parameter conversion. By measuring unbalanced S-parameters and converting them to mixed-mode parameters through mathematical relationships, the system achieves pure differential and common-mode measurements without the frequency limitations of hybrid circuits, extending the usable frequency range significantly.
3Reliability
If signal splitters are used to calibrate the VNA, then system error correction is achieved, but measurement accuracy deteriorates due to non-ideal splitter properties
Solution Approach 1:
The patent removes the signal splitter from the calibration process entirely. Instead of using a splitter to generate calibration signals, the method uses mathematical conversion of S-parameters measured at unbalanced ports to obtain mixed-mode parameters. This eliminates the accuracy degradation caused by non-ideal splitter properties while maintaining system error correction capabilities.
4Device complexity
If unbalanced VNA ports are used to measure balanced ports, then device complexity is reduced, but measurement accuracy of mixed-mode parameters deteriorates
Solution Approach 1:
The patent introduces mathematical conversion relationships as an intermediary between unbalanced S-parameter measurements and mixed-mode parameters. This mathematical mediator enables accurate extraction of differential and common-mode S-parameters from unbalanced measurements without requiring complex balanced measurement hardware, thus maintaining low device complexity while improving measurement accuracy.
Data Source
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AI summary
In a method for exciting port groups of a multiport measurement object (MO) with equal frequency and coherent travelling waves (a1, a2) that exhibit defined amplitude relationships and phase differences within each port group, the waves are each generated by one signal generator (401, 402) of a vector network analyzer (VNA) per measurement port (405, 406), the network analyzer (VNA) having unbalanced-to-ground measurement ports (405, 406). A system error correction of the unbalanced-to-ground bidirectional travelling waves is carried out in relation to the ports of the measurement object (MO) to obtain corrected waves. The amplitude and phase changes required to satisfy the desired amplitude and phase conditions in the signal generators (401, 402) are calculated from these corrected waves.