VNA Spur Elimination via Dynamic Null Selection
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Solution Overview
Problem
Vector network analyzers (VNAs) face challenges in accurately measuring electrical responses due to spurs, which introduce noise and affect the interpretation of measurements, especially when dealing with arbitrary bandwidths and specific null selection.
Innovation Solution
The method involves generating an intermediate frequency (IF) signal using a mixer and receiver, with parameters modified to ensure a null falls on the spur frequency, allowing for averaging of samples to reduce noise and eliminate spurs, while also shifting the IF signal frequency to offset crossover spurs from the default frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency sweeping is performed to measure electrical response, then measurement coverage is improved, but spurs are introduced that degrade measurement accuracy
Solution Approach 1:
The system pre-calculates and identifies spur frequencies before performing the measurement sweep. By knowing where spurs will occur in advance, the system can prepare averaging parameters and null positions to specifically target these frequencies, eliminating spurs before they corrupt the measurement data
Solution Approach 2:
The system converts the harmful spur signals into beneficial information by using them to define the positions of nulls in the averaging process. The spurs, instead of being mere noise, become the target frequencies for enhanced rejection through coherent averaging with strategically placed nulls
2Measurement precision
If averaging of multiple samples is performed, then noise reduction is improved, but measurement time increases
Solution Approach 1:
The system dynamically changes the averaging parameters based on the identified spur frequencies. By adjusting the number of averages and null positions according to the specific measurement conditions and spur locations, the system achieves optimal noise reduction with minimal measurement time, avoiding unnecessary averaging at frequencies where spurs are not present
3Measurement precision
If null positions are fixed in the averaging process, then system complexity is reduced, but spur elimination effectiveness decreases
Solution Approach 1:
The system implements dynamic null positioning in the averaging process. The null positions are not fixed but are calculated and adjusted based on the identified spur frequencies for each measurement sweep. This dynamic adaptation allows precise targeting of spurs while maintaining systematic control through automated calculation and implementation
4Measurement precision
If IF signal frequency is kept at default value, then device complexity is reduced, but crossover spur elimination is insufficient
Solution Approach 1:
The system pre-identifies crossover spur frequencies by calculating where the IF signal frequency intersects with potential spur frequencies. Before performing the measurement sweep, the system determines which frequencies require offset adjustments and pre-calculates the appropriate offset values, eliminating crossover spurs before they can corrupt the measurements
Solution Approach 2:
The system dynamically adjusts the IF signal frequency offset based on the identified crossover spur locations. By changing the IF frequency parameter selectively at frequencies where crossover spurs are expected to occur, the system eliminates these specific spurs while maintaining the default IF frequency elsewhere, achieving targeted spur elimination with minimal complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces the impact of spurs on measurements, providing accurate and noise-reduced data by aligning nulls with spur frequencies and adjusting IF signal frequencies to mitigate crossover spurs, thereby enhancing the reliability of VNA results.
Implementation Method 1
The measurement instrument is configured to generate, via the mixer, an intermediate frequency (IF) signal for use by the receiver from a radio frequency (RF) signal and a local oscillator (LO) signal
Data Source
AI summary
A method of eliminating spurs in measurements of an electrical response of a device under test (OUT) obtained uses a measurement instrument including a mixer and a receiver. The measurement instrument is configured to generate, via the mixer, an intermediate frequency (IF) signal for use by the receiver from a radio frequency (RF) signal and a local oscillator (LO) signal. Input is received from a user at the measurement instrument and includes start frequency and end frequency. Parameters for a frequency sweep are generated based on the input. A measurement for each frequency of the frequency sweep is calculated using averaging of a plurality of samples obtained at that frequency. Frequencies are identified within the frequency sweep at which spurs will occur due to the measurement instrument. The parameters for a frequency of the frequency sweep at which a spur will occur are modified so that a null for a measurement at the frequency falls on the spur.