# A Compact Circular Rectenna for RF-Energy Harvesting at ISM Band
## 1 Introduction
The advanced design system is used to create a single-stage Cockcroft-Walton rectifier that is constructed on an FR4 substrate with an L-shaped impedance-matching network. While the measured peak conversion efficiency was found to be 68% at a 5 dBm input signal power at 2.45 GHz with an output voltage of 3.24 V, the simulated peak conversion efficiency was achieved at 75.5% [14]. In [15], a rectangular patch engraved with fractal geometry is introduced to have high bandwidth and matching properties in the frequency range from 2.15 GHz to 2.9 GHz. A simple stub-matching rectifier circuit is investigated for high conversion efficiency and impedance matching with low input power density. The measured data show that the prototype rectenna provides a high efficiency of 64% at input 0 dBm and output DC 1.5 V. The authors of [16] describe a broadband energy harvesting rectenna which has been proposed for WSN application in the frequency band ranging from 1.8 GHz to 2.6 GHz. To improve the performance of the rectifier, an optimization method has been developed, based on which a prototype rectenna is generated to cover GSM1800, UMTS, and Wi-Fi bands. The conversion efficiency of the proposed rectenna shows 15% at \(-\)20 dBm input per source and 25% when all three sources are present with a total input power density of \(-\)20 dBm. In [17], a miniaturized dual-band antenna with C- and L-shaped slots is put forward for energy harvesting at 915 MHz and for transmitting the data at 2.45 GHz under implantable conditions. A simple voltage doubler circuit with HSMS 2852-rectifying diode is placed below the antenna to reduce the overall size of the rectenna. The highest conversion efficiency of 52% is observed at 5 dBm input and a 4.3 K\(\Omega\) load resistance is measured. Rectenna circuits require impedance matching. It maximizes power transmissions from the receiving antenna to the rectifier and reduces reflection losses. Impedance matching circuits are of different types, such as L-section, pi-section and T-section, of which the L-section is the simplest and most commonly used for matching networks due to its simple nature. In [18], a defective rectangular patch with a coplanar waveguide-fed rectenna is presented at 2.4 GHz. Edge slots are introduced in the ground plane near the feed to optimize and increase the bandwidth and gain 4.12 dBi. A hybrid triple rectifying network with an L-section match is attached to the antenna to obtain a conversion efficiency of 66.7% with 3.47 V output DC for 3 K\(\Omega\) load at 5 dBm input. In [19], a cross-shaped simple antenna with a gain of 8.6 dBi is matched directly to the rectifier network at 2.45 GHz, eliminating the second and third harmonics; therefore, the use of a band-pass filter is not needed to make the rectenna compact and simple. The impedance matching is obtained by varying the stub length and optimizing it to obtain a high conversion efficiency of 83% with a 1.4 K\(\Omega\) load at \(-\)7.7 dBm input. A microstrip resonator cell-inserted circular slot antenna is presented to suppress up to the third harmonic over a 3-8 GHz bandwidth, with a resonating frequency of 2.45 GHz. A new series-parallel rectifier [20] efficiency is increased by adding proper inductance under a low power input level. The proposed design has obtained a 70.2% conversion efficiency with a 1 K\(\Omega\) load. Rectifiers with compact structures, radial stub filters [21], and stub-matching circuits are designed using ADS [22]. Furthermore, rectifier configurations include single-diode, voltage doubler, and full-wave Greinacher rectifier [23]. Rectifier performance is greatly determined by the diodes, the capacitors used in the design, and also the number of stages. Based on the RF input power, operating frequency, and load, the number of stages are optimized to obtain the maximum output DC voltage. The power conversion efficiency of the rectifier changes with the change in the number of rectifier stages and with the change in the operating frequency from low to high.