Time Domain Voltage Measurement Calibration for RF Reflection
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Solution Overview
Problem
Existing methods for determining electric voltage and current in the time domain for RF signals on electric cables are not always exact, especially when using time domain measuring devices with non-zero reflection coefficients, leading to inaccuracies in measurement.
Innovation Solution
The method involves determining calibration parameters in relation to the frequency and reflection coefficients of the measuring device's inputs, using a directional coupler to decouple signal components, transforming them into the frequency domain, and then converting back into the time domain to determine accurate voltage and current values, accounting for the reflection coefficients at the measuring inputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If time domain measuring devices are used to determine electric voltage and current of RF signals, then measurement capability in time domain is achieved, but measurement precision deteriorates when the device has non-zero reflection coefficients
Solution Approach 1:
The patent applies parameter changes by determining calibration parameters that specifically account for the reflection coefficients of the measuring device. The method transforms the relationship between measured values and actual voltage/current by introducing frequency-dependent calibration parameters that compensate for the non-ideal reflection characteristics, thereby maintaining measurement accuracy despite using devices with non-zero reflection coefficients
Solution Approach 2:
The patent replaces direct time domain measurement with a hybrid approach that transforms measurements to the frequency domain for calibration compensation, then converts back to time domain. This substitution of measurement domain (from pure time domain to frequency-time domain hybrid) enables accurate compensation for reflection effects that would otherwise degrade measurement precision
2Measurement precision
If calibration parameters are determined in relation to frequency and reflection coefficients, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent applies preliminary action by performing calibration measurements in advance to determine the frequency-dependent calibration parameters and reflection coefficients. These calibration parameters are stored and then applied during actual measurements, separating the complex calibration process from the routine measurement process. This allows accurate compensation without adding complexity to the operational measurement system
Solution Approach 2:
The patent introduces calibration parameters as an intermediary element that mediates between the raw measurements from the directional coupler and the actual voltage/current values. These calibration parameters serve as a mathematical bridge that accounts for the non-ideal characteristics of the measuring device, enabling accurate results without requiring physical modification of the device
Data Source
AI summary
A method for determining an electric voltage u(t) and/or an electric current i(t) of an HF signal in an electrical cable on a calibration plane by measuring in the time domain. Using a directional coupler, a first portion v3(t) of a first HF signal is decoupled, fed to a time domain measuring device, and a second portion v4(t) of a second HF signal is decoupled. The signal portions v3(t), v4(t) are converted into the frequency domain, then absolute wave frequencies in the frequency domain are determined and converted into the electric voltage u(t) and/or the electric current i(t). In a previous calibration step, the calibration parameters are determined, and the absolute wave frequencies on the calibration plane are determined using the calibration parameters (e00,r(Γ3, Γ4), e01,r(Γ3, Γ4), e10,r(Γ3, Γ4), e11,r(Γ3, Γ4)), wherein Γ3, Γ4 are the reflection factors of the inputs of the time domain measuring device.