Next the first, second, and third mixed RF signals generated by frequency mixers 1181-1, 1181-2, and 1181-n may be processed (e.g., using a processor not shown in 
Multi-spectral interrogator 1170 may be manufactured in any suitable way. For example, in some embodiments, the interrogator 1170 may comprise a substrate having the transmit antennas 1173 and 1175, and receive antennas 1176-1, 1176-2, and 1176-n fabricated thereon. For example the substrate may comprise one or more conductive layers and the transmit and receive antennas may be patterned in the conductive layer(s). In some embodiments, the interrogator may comprise a semiconductor die mounted on the substrate and the receive circuitry (e.g., the frequency multipliers, frequency mixers, and amplifiers shown as part of interrogator 1170) may be integrated circuitry fabricated on the semiconductor die. In some embodiments, waveform generator 1171 and oscillator 1174 may also be integrated circuitry fabricated on the semiconductor die, but in other embodiments one or both of waveform generator 1171 and oscillator 1174 may be realized as discrete components on the substrate (e.g., as discrete components mounted on a PCB substrate).