A planar dual-band antenna design for RF energy harvesting applications

Past work on radio frequency (RF) energy harvester design mostly focused on harvesting RF energy in a single RF band [1, 2,]. While a significant portion of RF energy is concentrated in the communication band around 900 MHz, there is also abundant RF energy present in the band covering 1800 MHz to 2100 MHz. For example. Li [2011] demonstrated the design and implementation of a dual band RF energy harvester chip that has two cascade voltage multipliers in parallel and can operate at 900 and 1900 MHz bands. The chip can generate 1.2 V output DC voltage at 900 MHz for -19 dBm RF input power and 1.05 V output voltage at 2000 MHz for -18 dBm RF input power. The RF energy conversion efficiency is ~12% at 900MHz and ~8% at 2000MHz which is comparable with its single band counterparts at both frequencies in the literature. The design greatly increases the energy harvesting efficiency over two bands. It is found that the input impedance of the chip is ~ 50 ohm at 900 MHz, 26 ohm at 1.9 GHz, and 70+j10 ohm at 2 GHz. To operate the harvester chip in two bands, the antenna is required to be matched to the chip impedance at 900 MHz for one band and at either 1.9 GHz or 2GHz for the other band.