In the illustrative embodiment of FIG. 6B, receive antenna 654 is a folded dipole antenna configured to receive (e.g., from interrogator 600) RF signals having a center frequency of 61.25 GHz. The RF signals may be circularly polarized clockwise or counter-clockwise, in some embodiments. Although the antennas 654 and 656 are folded dipole antennas in the illustrative embodiment of FIG. 6B, in other embodiments, each of the antennas 654 and 656 may be of any other suitable type including any of the types described herein. Additionally, although the antennas 654 and 656 receive/transmit RF signals at 61.25 GHz/122.5 GHz in the illustrative embodiment of FIG. 6B, these antennas may be configured to receive/transmit at any other suitable (e.g., millimeter wave and/or microwave) frequencies f0/kf0, where the receive antenna 654 is configured to receive RF signals having a center frequency of f0 and the transmit antenna 656 is configured to transmit RF signals having a center frequency of kf0, which is a harmonic of f0. In the illustrative embodiment of FIG. 6B, the receive antenna 654 is a 2.5 mm wide folded dipole antenna and the transmit antenna 656 is a 1.25 mm wide folded dipole antenna.
