Multi-antenna techniques for enabling passive RFID tags and sensors at microwave frequencies

Multi-antenna techniques are typically avoided in passive RFID because of the large footprints required. However, the smaller footprints required at microwave frequencies such as the 5.8 GHz industrial, scientific, and medical (ISM) band allow the use of multiple antennas. Two new multi-antenna technologies are featured in this paper to provide power and communications to a passive wireless tag in the 5.8 GHz ISM band. A four-layer FR-4 PCB is presented, which uses a staggered-pattern charge collector (SPCC) and a retrodirective array phase modulator (RAPM). An SPCC is an energy harvester that has two independent antenna arrays. These arrays provide increased gain and beamwidth over a single-antenna source. A RAPM backscatters the reader-transmitted signal directly back to the reader and provides quadrature phase-shift keyed (QPSK) signaling.