Dual Frequency MIMO Rectenna with Two-Branch Rectifier and Common Power Storage Unit

A dual-frequency (433 MHz and 2.45 GHz) circularly polarized MIMO rectenna with dual-branch rectifier and a common power management unit is presented. For the lower frequency a dual-layer, four-element, monopole antenna array is implemented. The four monopoles are oriented along the perimeter of a square and are fed with 90° phase difference resulting in a circularly polarized antenna array. The total covered area is 80 x 80 mm2, and the maximum gain is 2.45 dBi. For the 2.45 GHz antenna, an elliptical patch is used implementing it in the middle of the square substrate that is used for the 433 MHz monopoles. As a result of the close proximity of the two radiating elements, the gain of the patch is enhanced to 6.2 dBi. Both antennas are probe-fed with two coaxial cables that pass through the antenna substrates. The coaxial cables are connected on the dual-branch, dual-frequency rectifiers. For the matching networks of the rectifiers, lumped elements are used for the 433 MHz rectifier, and hybrid, distributed and lumped elements, are used for the ISM band voltage-doubler. The combined use of both frequencies results in RF-to-dc efficiency up to 70% for input power close to 0 dBm. The dual rectifiers have a common load since they are terminated with a common power management unit circuit. The commercially available e-peas AEM30940 RF is considered as the PMU circuit. It presents cold start-up from 380 mV and 3 μW, and is able to supply low-voltages (from 1.2 to 1.8 V) suitable for most microcontrollers and also “high” voltages ranging from 1.8 V up to 4.1 V.