Extending Test Instrument Calibration Range via Frequency Interpolation
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Solution Overview
Problem
Conventional calibration techniques for test instruments, such as vector network analyzers, are limited in their ability to accurately calibrate phase response across extended frequency ranges, particularly below 55 MHz or above 67 GHz, and cannot interpolate or extrapolate between discrete cardinal frequencies.
Innovation Solution
A method that involves determining a first response of a calibration device over a specific set of operating ranges, deriving a second response based on the first, measuring the second response, and calculating correction factors to extend the calibration range beyond the limitations of the calibration standard, using a phase reference device and an unknown mixer with a smooth response to interpolate or extrapolate across frequency ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional calibration techniques are used with a phase reference device, then calibration accuracy is achieved within the limited frequency range (55 MHz to 67 GHz), but calibration cannot be performed outside this range or between discrete cardinal frequencies
Solution Approach 1:
The frequency range is divided into multiple segments: a first frequency range where direct calibration using the phase reference device is performed, and a second frequency range where calibration is extended through interpolation or extrapolation based on the first range. This segmentation allows the calibration system to methodically expand its coverage while maintaining accuracy in the core range.
Solution Approach 2:
The calibration process performs preliminary calibration measurements within the reliable frequency range of the phase reference device first. These preliminary results are then used as a foundation to derive correction factors for frequencies outside the direct measurement range, enabling extended calibration without requiring the phase reference device to operate beyond its validated range.
2Ease of manufacture
If the calibration is restricted to discrete cardinal frequencies generated by the harmonic comb generator, then the calibration process is straightforward, but the calibration cannot be performed at intermediate frequencies between cardinal frequencies
Solution Approach 1:
The system introduces an intermediary computational process that uses the discrete cardinal frequency measurements as reference points. Through interpolation algorithms, this intermediary process generates correction factors for intermediate frequencies that lie between the discrete cardinal frequencies, thereby extending calibration coverage without adding physical hardware at every frequency point.
3Measurement precision
If the phase reference device is used as the calibration standard, then phase response calibration can be performed, but the calibration is limited to the device's specific operating range and cannot be extrapolated
Solution Approach 1:
The system changes the frequency parameter beyond the phase reference device's rated operating range by using mathematical extrapolation. Correction factors are calculated for frequencies outside the device's specified range based on the measured response within the valid range, allowing the calibration system to operate at extended frequencies without physically modifying or replacing the phase reference device.
Data Source
AI summary
A method of calibrating a test instrument comprises determining a first response of a calibration device on the test instrument over a first set of operating ranges, determining a derived second response of the calibration device on the test instrument over a second set of operating ranges based on the first response, measuring the second response of the calibration device on the test instrument over the second set of operating ranges, and determining correction factors of the test instrument for the second set of operating ranges based on a comparison between the measured second response and the derived second response.