Spectral Stitching Discontinuous Spectra Using Pilot Tones
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Solution Overview
Problem
Existing measurement systems struggle to accurately measure periodically modulated signals with bandwidths exceeding the receiver's bandwidth, particularly in cases where the output signal of a device under test contains harmonics, leading to incomplete characterization due to spectral regrowth and limited measurement bandwidth.
Innovation Solution
The method involves using pilot tones and a comb signal with known phase differences to downconvert and measure the output signal in multiple frequency segments, adjusting phases to stitch together measurements across overlapping portions, and utilizing a local oscillator to change frequencies for each conversion, ensuring accurate amplitude and phase measurements despite limited receiver bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a receiver with limited bandwidth is used to measure periodically modulated signals, then the device complexity is reduced and ease of operation is improved, but the measurement precision deteriorates because the receiver cannot capture the full bandwidth of the signal including harmonics
Solution Approach 1:
The patent divides the broadband signal measurement into multiple narrowband segments. A frequency tuner sequentially tunes the receiver to different frequency segments of the periodically modulated signal, and a spectrum analyzer measures each segment separately. The measurements from all segments are then combined to reconstruct the complete spectrum, enabling accurate measurement of wideband signals using a narrowband receiver.
Solution Approach 2:
The patent applies preliminary frequency translation by mixing the input signal with a local oscillator signal before measurement. This downconverts the high-frequency broadband signal to a lower intermediate frequency, making it suitable for measurement by the narrowband receiver while preserving all spectral information including harmonics.
2Ease of operation
If the receiver bandwidth is reduced to simplify the measurement system, then the ease of operation improves, but the measurement precision deteriorates due to incomplete spectral coverage
Solution Approach 1:
The patent creates a universal measurement system that can measure signals of any bandwidth by combining a narrowband receiver with a frequency tuner. The system performs multiple measurements at different frequency segments and combines them to achieve complete spectral coverage, making the simple narrowband receiver capable of measuring wideband signals through its multi-functional operation.
Solution Approach 2:
The patent introduces dynamic frequency tuning capability to the narrowband receiver. The frequency tuner dynamically adjusts the receiver's center frequency to sequentially measure different segments of the broadband signal. This dynamic adaptation allows the fixed narrowband receiver to cover the entire wideband signal spectrum through multiple sequential measurements.
3Measurement precision
If multiple harmonics are measured simultaneously, then the measurement precision of phase-sensitive characteristics improves, but the device complexity increases due to the need for wideband measurement capability
Solution Approach 1:
The patent segments the measurement process by frequency, measuring each harmonic component in separate frequency segments using the narrowband receiver. The frequency tuner positions the receiver at each harmonic frequency, and the spectrum analyzer measures the phase and amplitude of that specific harmonic. This segmented approach enables precise multi-harmonic measurement without requiring a complex wideband receiver.
Solution Approach 2:
The patent employs periodic frequency tuning to sequentially measure different harmonics of the periodically modulated signal. The frequency tuner periodically sweeps through the frequency segments corresponding to different harmonics, and the spectrum analyzer captures phase information at each segment. This periodic measurement approach reconstructs complete multi-harmonic phase characteristics using a simple narrowband receiver.
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 allows for accurate measurement of phase-sensitive characteristics like error-vector-magnitude (EVM) across multiple harmonics, even when the receiver's bandwidth is insufficient, by correcting for phase shifts and stitching together measurements from overlapping spectral segments.
Implementation Method 1
downconverting a frequency of the output signal to an intermediate frequency by mixing the output signal with a local oscillator signal
Implementation Method 2
measuring an amplitude and phase of the intermediate frequency signal as a function of frequency for each of the sequentially converted portions of the output signal spectrum segment
Implementation Method 3
adjusting the measured phase of the intermediate frequency signal as a function of frequency for one or more of the sequentially converted portions of the output signal spectrum segment using the measured phases of the converted first and second pilot tones to produce phase-adjusted measurements of the intermediate frequency signal
Data Source
AI summary
A system and method sequentially measure the amplitude and phase of a signal in each of two or more noncontiguous spectrum segments (e.g., harmonics) which each include two or more portions which together span the spectrum segment, using a local oscillator (LO) signal whose frequency and phase change for each measurement. The measured phase of the signal for at least one of the portions in each spectrum segment is adjusted to account for the change of phase in the LO signal from measurement of one portion to another, using phases of one or more pilot tones measured in each portion. The phase-adjusted measurements of the output signal in the various portions are stitched together to determine the amplitude and phase of the output signal across the spectrum segment. The phase relationships between the spectrum segments are determined from phases of comb teeth of a comb signal measured in each spectrum segment.