Spectral Stitching Method to Increase Instantaneous Bandwidth in Vector Signal Analyzers

An apparatus for processing a signal, the apparatus comprising:

• a signal splitter configured to receive an analog signal, and output a plurality of copies of the analog signal;
• a plurality of output ports, each of the output ports configured to provide to a respective vector signal analyzer (VSA) a respective copy of the analog signal;
• a plurality of input ports, each of the input ports configured to receive from a respective VSA a respective digital signal, wherein the respective digital signal comprises a digitized version of a respective frequency band of the analog signal, the respective frequency band having a respective center frequency and having a region of overlap with at least one other frequency band received by another of the input ports, wherein the respective center frequency of the respective frequency band has a respective frequency offset from an aggregate center frequency of an aggregate frequency band, the aggregate frequency band comprising a combination of the frequency bands of the received digital signals, and wherein the respective VSA is phase-locked and time-synchronized with respect to the VSAs of the other input ports;
• a plurality of parallel signal processing pathways, each of the parallel signal processing pathways configured to:
• receive a respective digital signal from one of the input ports;
• frequency-shift the respective digital signal such that the respective center frequency is offset from baseband by the respective frequency offset;
• adjust gain and phase of the respective digital signal, wherein said adjusting gain and phase of the respective digital signals is configured to cause a sum of the digital signals to have a continuous frequency response over the aggregate frequency band;
• and
• a summing unit configured to sum the outputs of the plurality of parallel signal processing pathways to obtain a composite signal.

A method for calibrating a signal processing system including at least a first vector signal analyzer (VSA) and a second VSA, the method comprising:

• providing to the first VSA a first component signal, the first component signal comprising a first frequency band within an aggregate frequency band of an input signal, the aggregate frequency band having an aggregate center frequency, and the first frequency band having a first center frequency at a first frequency offset from the aggregate center frequency;
• providing to the second VSA a second component signal, the second component signal comprising a second frequency band within the aggregate frequency band of the input signal, the second frequency band having a second center frequency at a second frequency offset from the aggregate center frequency, the second frequency band having a region of overlap with the first frequency band, the region of overlap containing a calibration tone, wherein the second VSA is phase-locked and time-synchronized with respect to the first VSA;
• digitizing the first and second component signals;
• frequency shifting each of the first and second component signals, after said digitizing, such that the first center frequency is offset from baseband by the first frequency offset and the second center frequency is offset from baseband by the second frequency offset;
• computing a complex calibration constant based on a magnitude ratio and a phase difference, wherein the magnitude ratio is determined by a magnitude of the calibration tone measured by the first VSA and a magnitude of the calibration tone measured by the second VSA, wherein the phase difference is determined by a phase of the calibration tone measured by the first VSA and a phase of the calibration tone measured by the second VSA;
• storing the complex calibration constant in memory, wherein the complex calibration constant is useable to correct phase and gain mismatch between the first VSA and the second VSA.