In the second calibration step, channel 2 is activated and channels 1, 3, and 4 receive calibration signals. The calibration signal level is limited by two aircraft Minimum Operational Performance Standards (MOPS) requirements.17 The first requirement is that when the transmitter is in an inactive state, the RF power at the antenna terminal should not exceed -70 dBm. The second requirement is that the maximum receiver sensitivity is -99 dBm. These limits set the dynamic range of the calibration signal between -99 dBm and -70 dBm. Table 3 illustrates the performance of different antenna modules.

A quick glance at Table 3 shows that the active antenna module can provide good performance (when properly calibrated) compared to multiple antenna systems implemented with and without phase shifters, as well as with systems using the SBFN with a five monopulse-element antenna system with four receive channels. The active antenna approach provides four receive channels and antenna terminals with moderate bandwidth and avoids an additional phase shifter.

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