Next the first, second, and third mixed RF signals generated by frequency mixers 1118-1, 1118-2, and 1118-n may be processed (e.g., using a processor not shown in FIG. 11A, but which may be in or external to interrogator 1100) to determine the distance between the interrogator 1100 and target device 1150. This may be done in any suitable way. For example, in some embodiments, the first, second and third mixed RF signals may be combined to generate a single RF signal indicative of the distance between the interrogator 1100 and target device 1150. In some embodiments, the mixed RF signals may be combined in the frequency domain. For example, the mixed RF signals may be apodized (e.g., windowed with a suitable windowing function) and added to one another in the frequency domain to generate the combined signal. As another example, the mixed RF signals may be used to estimate a combined RF signal using bandwidth extension techniques. Any of the foregoing combination techniques may be implemented in the time-domain and/or in the frequency domain. Regardless of how the mixed RF signals are combined to generate a combine RF signal, the combined RF signal may be used to determine the distance between the interrogator 1100 and target device 1150. This may be done by performing an inverse Fourier transform on the combined RF signal and identifying the location of the peak, which location indicates the time of flight between interrogator 1100 and target device 1150, and convert the location of the peak to an estimate of the distance between the interrogator and target device, or in any other suitable way.
