As described above, receive-only interrogator 1434 operates phase coherently with master interrogator 1432. For example, as shown in FIG. 14D, receive-only interrogator 1434 is configured to generate RF signals that are phase coherent with the RF signals generated and transmitted by the master interrogator 1432. To this end, receive-only interrogator 1434 includes waveform generation circuitry 1464 for generating frequency-modulated waveforms using a direct digital synthesizer in a “swept reference” approach, which was described above with reference to FIG. 13A. However, unlike the waveform generation circuitry 1300 shown in FIG. 13A, the waveform generation circuitry 1464 replaces the DDS 1310 with shared direct digital synthesizer 1440 (which is shared among all the receive-only interrogators 1434, 1436, and 1438 shown in FIG. 14B). As shown in FIG. 14D, the shared DDS 1440 is coupled to frequency multiplier 1308 via line 1442.
