GPS World, September 2013
Galileo and BeiDou GNSS DESIGN FIGURE 3 Measurement setup overview FIGURE 4 Gain of the measurement system after the feed over 14 hours are needed The injection path from the signal generator to the couplers and the direct paths are characterized by network analyzer NWA measurements Based on the chirp and NWA measurements the transfer function of the system is calculated to derive the gain and phase information To determine the calibration curve over the frequency range from 10 GHz to 18 GHz a set of overlaying chirps with different center frequencies is injected into the signal paths and combined within the analysis FIGURE 4 and FIGURE 5 show the results of the wideband calibration of gain and phase Is it enough to determine the gain only once If we assume that there is no aging effect of the elements and the ambient conditions like temperature are constant the gain should not change In reality the behavior of the system is not constant FIGURE 6 shows the temperature within the cabin during a failure of its air conditioning system FIGURE 7 shows the corresponding gain of the measurement system during the temperature change in the cabin of about 5 Celsius Clearly it www gpsworld com September 2013 GPS World 37
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