After receiving the target device's responsive RF signal, interrogator 1432 may use the responsive RF signal and a version of the transmitted RF signal to generate a first mixed RF signal indicative of the distance between the interrogator 1432 and the target device. Each of receive-only interrogators 1434, 1436, and 1438 may receive, via lines 1442, the reference signal generated by the DDS 1440, and generate using the received reference signal, a local version of the RF signal transmitted by master interrogator 1432. Next, each of receive-only interrogators 1434, 1436, and 1438 may receive a respective responsive RF signal from the target device and may generate, using the received responsive RF signal and a respective local version of the transmitted RF signal, a respective mixed RF signal indicative of the distance between the receive-only interrogator and the target device.