Group Delay Determination Using VNA Phase Slope
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Solution Overview
Problem
Conventional oscilloscopes are inefficient and costly for calibrating time errors in measurement instruments due to their limited scalability and requirement for manual port reconfiguration, leading to measurement errors and inefficiencies compared to vector network analyzers (VNAs).
Innovation Solution
A system for determining group delay between periodic RF signals in the frequency domain using narrow-band coherent receivers and a vector network analyzer, allowing for time synchronization without processing signals in the time domain, thereby increasing efficiency and reducing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an oscilloscope is used to measure time delay between periodic RF signals, then timing comparison can be performed, but measurement efficiency is low and cost is high
Solution Approach 1:
The patent transforms the measurement approach from time domain to frequency domain by changing the operating parameters of the measurement instrument. VNAs inherently operate in the frequency domain, measuring magnitude and phase of sinusoidal signals at different frequencies. This parameter change allows the system to determine group delay (time delay) through phase slope calculation without requiring time-domain processing, thereby improving measurement efficiency while maintaining accuracy.
Solution Approach 2:
The patent replaces the mechanical/time-domain measurement system (oscilloscope with pulse envelope comparison) with a frequency-domain measurement system (VNA with phase slope measurement). This substitution eliminates the need for time-domain signal processing and manual port reconfiguration, significantly improving productivity while maintaining measurement precision through mathematical transformation of the measurement approach.
2Measurement precision
If an oscilloscope is used for calibration, then time error correction can be performed, but the measurement reference plane requires modification using adapters and scalability is limited to four ports
Solution Approach 1:
The patent leverages the universal capability of VNAs to perform multiple functions including time error correction, group delay measurement, and calibration across multiple ports simultaneously. VNAs are designed with integrated calibration capabilities that can handle more than four ports without requiring physical reconfiguration, making the measurement system adaptable to instruments with any number of ports while maintaining measurement precision through built-in compensation for external connectors, cables and adapters.
3Adaptability or versatility
If manual port reconfiguration is performed on an oscilloscope, then all ports can be measured, but measurement errors increase due to connector/cable repeatability
Solution Approach 1:
The patent implements preliminary calibration actions using VNA's integrated calibration capability before measurements are taken. The VNA performs calibration measurements that compensate for the effects of external connectors, cables and adapters in advance. This preliminary action establishes accurate measurement reference planes for all ports simultaneously, eliminating the need for manual reconfiguration during measurement and preventing measurement errors from connector/cable repeatability issues.
Data Source
AI summary
A method of determining group delay between periodic radio frequency (RF) signals received at a narrow-band coherent receivers includes receiving a first periodic RF signal at a first coherent receiver in the frequency domain, receiving a second periodic RF signal at a second coherent receiver in the frequency domain, which is delayed with respect to the first periodic RF signal, the first and second periodic signals having the same period and carrier frequency; determining a cross-spectrum signal of the first and second periodic RF signals in the frequency domain, the cross-spectrum signal including amplitudes and phases versus frequency; calculating a slope of phase of the cross-spectrum signal at frequencies over at least a portion of a bandwidth of the cross-spectrum signal; and determining a group delay between the first and second periodic RF signals to be the slope of phase of the cross-spectrum signal.