A target device that is configured to transmit RF signals at multiple different harmonics of a center frequency in response to receiving RF signals having the center frequency may be called a “multi-spectral target device.” An interrogator device configured to transmit, to a target device, RF signals having a center frequency and to receive, from the target device, RF signals at multiple different harmonics of the center frequency may be called a “multi-spectral interrogator device.” A multi-spectral target device is not limited to responding with RF signals only at harmonics of a center frequency of a received RF signal and, in some embodiments, may respond at multiple different frequencies each of which depends on the center frequency in some way. For example, each of the multiple different frequencies may be: (1) a respective harmonic of the center frequency (as described with reference to