Pulsed RF Measurement Resolution via Phase Coherent DFT
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Solution Overview
Problem
Existing methods for pulsed radio frequency (RF) measurements using vector network analyzers face challenges with low duty cycles leading to energy loss and degraded dynamic range, and direct time domain acquisitions suffer from limited resolution and noise sensitivity, making them ineffective for high accuracy below 8 samples.
Innovation Solution
The method involves generating a pulsed RF test signal, shifting the phase of a local oscillator signal, sampling over multiple pulses, and applying a discrete Fourier transform or short-time discrete Fourier transform to improve resolution while maintaining the ADC clock rate, allowing for phase coherence and dynamic nonlinear fitting to enhance measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If localizing the central line of the pulsed spectrum and processing normal VNA measurements is used, then phase measurements can be obtained, but RF power loss occurs and dynamic range degrades for low duty cycles
Solution Approach 1:
The patent changes the parameter of LO signal phase by introducing a prescribed phase shift between successive pulses. This parameter change enables the system to maintain measurement capability while improving power utilization efficiency, thereby resolving the contradiction between phase measurement capability and RF power loss.
2Adaptability or versatility
If direct time domain acquisitions of IF signals are used, then duty-cycle-independent processing is achieved, but profiling resolution is limited to about 8 samples
Solution Approach 1:
The patent segments the measurement process by applying DFT to multiple individually processed pulses rather than treating the entire dataset as a single time-domain acquisition. This segmentation allows each pulse to be processed independently with high resolution, while maintaining duty-cycle independence through the phase-shifted sampling approach across multiple pulses.
Solution Approach 2:
The patent transitions from one-dimensional time-domain processing to two-dimensional processing by introducing the pulse index dimension. By applying DFT across both time samples within each pulse and across multiple pulses with phase shifts, the system achieves resolution beyond the traditional 8-sample limit while maintaining adaptability to various duty cycles.
3Measurement precision
If reducing profiling width is attempted for higher resolution, then measurement accuracy improves, but noise sensitivity increases rapidly below 8 samples
Solution Approach 1:
The patent introduces feedback through the phase-coherent processing of multiple pulses. By maintaining phase coherence across pulses and using the known phase shifts in the DFT processing, the system can coherently integrate signals while incoherently averaging noise, thereby achieving high resolution with reduced noise sensitivity even for narrow profiles.
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 achieves improved profiling resolution, reducing measurement width to as low as 5 ns, offering 2-8 times better resolution than traditional DFT techniques with comparable accuracy and maintaining phase coherence.
Implementation Method 1
A phase of the LO signal is shifted by a prescribed amount while generating the IF signal
Implementation Method 2
An intermediate frequency (IF) signal is generated using a local oscillator (LO) signal
Implementation Method 3
A discrete Fourier transform (DFT) is then applied to the constructed measurements
Data Source
AI summary
A method for obtaining improved resolution pulsed radio frequency (RF) measurements with phase coherence for a device under test (DUT) using a vector network analyzer (VNA) includes generating a pulsed RF test signal, transmitting the pulsed RF test signal to the DUT and receiving a signal from the DUT at the VNA in response to the pulsed RF test signal. An intermediate frequency (IF) signal is generated using a local oscillator (LO) signal. A phase of the LO signal is shifted by a prescribed amount while generating the IF signal. The IF signal is then sampled over multiple pulses and measurements are constructed from the measurements. A discrete Fourier transform (DFT) is then applied to the constructed measurements.