The RF signals may be circularly polarized clockwise or counter-clockwise. Although the antennas 604 and 606 are patch antennas in the illustrative embodiment of FIG. 6A, in other embodiments, each of the antennas 604 and 606 may be of any other suitable type including any of the types described herein. Additionally, although the antennas 604 and 606 transmit/receive RF signals at 61.25 GHz/122.5 GHz in the illustrative embodiment of FIG. 6A, these antennas may be configured to transmit/receive at any other suitable (e.g., millimeter wave and/or microwave) frequencies f0/kf0, where the transmit antenna 604 is configured to transmit RF signals having a center frequency of f0 and the receive antenna 606 is configured to receive RF signals having a center frequency of kf0, which is a harmonic of f0. In the illustrative embodiment of FIG. 6A, the transmit antenna 604 is a 2.5 mm×2.1 mm patch antenna and the receive antenna is a 1.25 mm by 0.86 mm patch antenna.
