Calibration Methods
The 89410A vector signal analyzer and the 71910A receiver are both capable of
self calibration. To obtain the best system performance, the instruments must
be calibrated together.
The IBASIC example program calibrates both instruments as a system. The
program compensates for system-induced errors, such as unequal cable lengths
for the I and Q signals. It also fine tunes factory calibrations, such as
quadrature, for optimal performance.
The calibrations affect more than just amplitude accuracy. As shown in the
following illustration, calibrations also improve the dynamic range of the
system.
Calibration Improves Accuracy and Dynamic Range
To perform the calibrations, the IBASIC example program uses the 300 MHz
calibrator built into the microwave spectrum analyzer. The program measures
the magnitude and phase of the calibration signal while adjusting the center
frequency of the microwave spectrum analyzer. It also measures the amount of
residual DC in the I and Q signals. From these measurements, the program
determines the IQ gain imbalance, IQ magnitude error, IQ delay mismatch, IQ
quadrature error and the DC offset. It then adjusts both instruments to
minimize the effects of the errors.
Calibrations provide
better accuracy and
improve dynamic range.
Upper trace shows
spectrum of 300 MHz
calibrator as measured
before system
calibrations. Lower trace
shows measurement of
same signal after system
calibration.
Extending Analysis to 26.5 GHz with 20 MHz Information Bandwidth
16 - 18
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