As shown in FIG. 6A, interrogator 600 comprises a substrate 602 having a differentially feed circular polarized transmit antenna 604 and a differential feed circular polarized receive antenna 606 disposed thereon. The interrogator 600 further comprises semiconductor die 608 having transmit and receive circuitry integrated thereon. The transmit and receive circuitry integrated with the semiconductor die 608 is differentially coupled to antenna 602 via lines 609a and 609b. The transmit and receive circuitry on the semiconductor die is also differentially coupled to antenna 606 via lines 610a and 610b.
Substrate 602 may be of any suitable type described herein including with reference to substrate 505 of FIG. 5A and, for example, may comprise a printed circuit board (PCB) and/or be manufactured from any suitable printed circuit board materials or other materials capable of supporting propagation of RF signals in a desired range of frequencies. In some embodiments, the substrate 602 may include a frequency selective surface and/or absorbent coating to reduce harmonic coupling between the transmit antenna 604 and the receive antenna 606. Examples of frequency selective surfaces and absorbent coatings are described herein. In the illustrative embodiment of FIG. 6A, the substrate 602 may be 4 mm×5 mm.
In the illustrative embodiment of FIG. 6A, transmit antenna 604 is a patch antenna configured to transmit circularly polarized RF signals having a center frequency of 61.25 GHz.
