Methods, systems, and low power retro-directive RF tags for localization

A method of operating a frequency modulated continuous-wave (FMCW) radar, the method comprising:

• transmitting a plurality of first signals from a plurality of antennas of the FMCW radar, wherein each of the plurality of first signals comprises a continuous wave with a frequency that linearly varies over time across a defined bandwidth and duration;
• receiving, via the plurality of antennas, a plurality of second signals that include asynchronously modulated retro-directive responses, each asynchronously modulated retro-directive response being generated by at least one remote radio frequency tag located remotely from the FMCW radar, wherein each asynchronously modulated retro-directive response is produced by retro-directively reflecting a respective first signal of the plurality of first signals back toward the FMCW radar in an asynchronously modulated form;
• generating difference Intermediate Frequency signals by comparing the plurality of first signals and the plurality of second signals;
• and
• performing a first transform operation on the difference Intermediate Frequency signals to detect and identify a presence of the asynchronously modulated retro-directive responses in the difference Intermediate Frequency signals, wherein the FMCW radar is configured to localize the at least one remote radio frequency tag based on the asynchronously modulated retro-directive responses.