In this letter, a low-profile circularly polarized (CP) chamfered rectangular dielectric resonator antenna (RDRA) is designed and investigated for radio frequency energy harvesting (RFEH) applications. The proposed modified RDRA comprises of dielectric resonator (DR) made up of Alumina material (& epsilon;(r) = 9.9) mounted on the PEC ground plane. Dual unequal triangular-shaped vertical slits are engraved on the rectangular DR for generating the orthogonal modes with CP characteristics. The optimized antenna offers an impedance bandwidth (IBW) of 51.4% (2.25-3.81 GHz) and axial ratio bandwidth (ARBW) of 14.8% (3.25-3.77 GHz), respectively. The peak realized gain and maximum radiation efficiency are 7.18 dBi and 97.8% in desired frequency bands. Due to the wide impedance and AR bandwidths with realized gain and radiation efficiency, the optimized antenna is suitable for integration with a rectifier circuit for RF energy harvesting applications. A rectifier circuit with a single shunt diode topology is also designed for rectification purposes. The rectifier achieved 67.16% RF-DC power conversion efficiency (PCE) at 3.5 GHz and 5dBm input power. At 0dBm input power, the rectifier achieved 60.26% PCE. The effective input power range, during which the PCE maintains above 50%, is calculated to be 15.2 dBm from -3.5 to 11.7 dBm.

Microwave power transfer (MPT) is the technique to transfer radio-frequency (RF) energy from one place to another place without using wire in the form of microwave signals. At the receiver end, an antenna circuit is needed to receive the signal. A circuit known as a rectifier is also needed to convert this received microwave energy into DC energy to store. The conversion takes place using a nonlinear rectifying device called a Schottky diode. In this work, a broadband rectifier with a high power conversion efficiency and high-power handling capability is reported. For this purpose, a Schottky diode having a 15V breakdown voltage has been chosen. The rectifier covers the GSM 1.8, LTE 2.1, and Wi-Fi 2.45 GHz bands. The rectifier has a sensitivity of -10 dBm and has power conversion efficiency (PCE) greater than 65% from 1.73 to 2.65 GHz at a 20 dBm input power level. The PCE exceeds 60% from 1.645 to 2.54 GHz at 13 dBm. The maximum PCE reached 78.4% at 2.47 GHz at 20 dBm input power.

In this paper, a new rectenna system for RF energy harvesting applications has been proposed. The antenna offers 5.8327 dB of gain. The results obtained demonstrate that the suggested antenna offers a substantial gain of 5.8327 dB and an impedance bandwidth of 1.7183 GHz. The rectifying component incorporates a single series diode (SSD) design, which accurately matches the input impedance by employing L-shaped transmission line matching network. This design choice allows for the efficient utilization of the majority of the received power. The results obtained from the simulation demonstrate that the rectenna achieved a notable conversion efficiency of 68.103% when exposed to a load of 2 kΩ at 3.5 GHz operating frequency and an input power of 5 dBm. The produced output DC voltage is 2.075 V.

Microwave power transmission (MPT) is a popular technique to provide wake-up power to any low-power devices located at remote locations. A rectenna circuit is therefore needed to capture the RF signal from the surroundings and convert it to electrical DC. This DC power can be utilized to feed the low-power sensors. For efficient performance of rectenna circuits, an efficient rectifier is required. For this purpose, a dual-band rectifier operating at GSM1.8 and WiFi/WLAN2.45 GHz is proposed in this paper. A single diode in series topology and a dual-band matching network have been utilized for RF to DC rectification. The rectifier achieved RF to DC power conversion efficiency (RF-DC PCE) of 61.4% and 54.9% at 1.8, and 2.45 GHz, respectively at 0 dBm. At -30 dBm rectifier has RF-DC PCE of 1.87% and 1.2% at 1.8 and 2.45 GHz respectively. Also, the RF-DC PCE of the rectifier exceeds 50% for the two bands 1.71-1.92 GHz and 2.26-2.52 GHz at 0 dBm.

The microwave energy-harvesting (MEH) and microwave power transfer (MPT) technologies have become the most emerging areas of research nowadays. The microwave rectifier circuit is the bottleneck of both the MEH and MPT systems. The efficiency of the system depends on the power conversion efficiency (PCE) of the rectifier. Due to the recent advancement of the fifth-generation communication system, it is desirable to propose an efficient rectifier operating at sub-6 GHz 5G bands. A dual-band rectifier circuit is designed and demonstrated for MEH/MPT purposes, specifically at sub-6 GHz 5G frequency bands. The dual-band matching is achieved by using a stepped impedance transmission line. The rectifier covers N78 (3.3–3.6 GHz) and N79 (4.8–5.0 GHz) bands. Peak PCE of 67.6% @ 3.5 GHz and 56.8% @ 4.9 GHz are achieved. For validation purpose, the rectifier is fabricated and characterized and measured results show good agreement with simulated results.

RF energy harvesting (RFEH) is an emerging technique in the field of wireless technology. The key components of this system are receiving antenna, matching network, and rectifier circuit. A rectifier circuit based on a tuned matching circuit is demonstrated in this paper for RFEH applications. The topology of this rectifier circuit is suitable for selecting a wide range of operating frequency bands, realized by changing the value of the inductor in the matching network. For validation purpose, a rectifier has been designed, developed, and tested at 2.45 GHz. The rectifier achieved peak power conversion efficiency (PCE) of 64.5% at 0 dBm. The PCE is higher than 50% for input power in the range of -8.5-2 dBm. The proposed rectifier has a compact size of 20 x 15 x 1.524 mm(3). By changing the value of the inductor in the matching network this rectifier can be redesigned for any other operating frequency in the range of 0.6-2.6 GHz.

This article presents an overview of dielectric resonator (DR)-based sensing elements and their applications in RF energy-harvesting (RFEH) and wireless power transmission (WPT) systems. With increased wireless applications, the demand for electrical energy goes up, thereby enabling the development of various energy sources. RF energy is widely available and the most efficient energy source. Although DR antennas (DRAs) have been studied extensively in the last few decades, they have not been employed in RFEH and WPT applications. The intention of the proposed article is 1) to provide an overview of the DRA for RFEH and WPT applications; 2) to accommodate various performance enhancement approaches for the DRA; and 3) to highlight the research gap for developing a complete rectenna system that helps future researchers. We believe that this survey may help the DRA.

In this article, we present an overview of the 5G rectifying antenna and its primary elements for applications in millimeter-wave (mm-wave) energy harvesting (EH) and wireless power transmission (WPT). The wide spectrum available for 5G communication bands have attracted significant attention for extensive applications. The power received by the harvesting antenna relies on the size of the antenna. Hence, the realization of antenna and rectenna systems with good efficiency at 5G mm-wave is a challenge. This review article highlights the recent advances in 5G rectenna systems for different applications at the component and structure levels. The primary objectives of the article are 1) to explore the potential advances of mm-wave rectenna systems and the feasibility of their designs to attain desired characteristics and 2) to present a comparative assessment of performance parameters of existing rectenna systems.

Radio frequency energy harvesting (RFEH) approach is found to be an appropriate solution for providing various smart city services in a better way by extending the lifetime of sensing nodes incorporated in the smart city. A novel compact hexagonal-shaped microstrip radiator for RFEH applications is presented for smart city applications. The proposed antenna, designed at 1.6mm thick low-cost FR4 substrate sheet, operates 1.8 GHz (1.70-1.84 GHz), 2.6 GHz (2.54-2.68 GHz), and 3.5 GHz (2.96-4.64 GHz) covering newly released LTE and 5G bands in addition to the GSM1800 band. A ground loaded slot introduced in the ground plane causes the second resonant band. Further, introducing a notch on to the slot-loaded ground plane produces the desired resonances with improved impedance matching and as well as impedance bandwidth performances at resonating bands of the proposed antenna with reducing antenna dimensions. The proposed configuration having a dimension of 100×100×1.6 mm 3 . The implemented design provided a gain of 6.41 dBi, is maximum at the operating frequency.

A dual-band rectifier is presented for RF energy harvesting (RFEH) and microwave power transfer (MPT) applications. Starting with a single-band rectifier, the second band is added by utilizing a half-wavelength transmission line (HWTL) in the matching network (MN). A series diode topology using HSMS-2860 Schottky diode is used for power conversion. The rectifier simultaneously harvests the RF energy with power conversion efficiency (PCE) of 54.9% and 42.3% and output voltage of 1.4 and 1.242 V at 0-dBm input power for 3.5-GHz 5G band and 5.8-GHz Wi-Fi band, respectively.

In this article, the characteristics of four spiral-facet structures are studied for RF energy-harvesting (RFEH) applications for increasing the harvesting power from the surrounding atmosphere. A rectangular dielectric resonance antenna (RDRA) is selected and placed above an FR4-epoxy substrate. Metallic rectangular spirals are then placed on the dielectric resonator (DR) surface to create resonances with insensitive polarization characteristics. The proposed spirals help provide wideband/multiband characteristics at 4.85, 5.0, 5.5, 5.8, and 6.25 GHz that covers 5G 4.9, WLAN 5.0, WLAN 5.5, Wi-Fi 5.8, and Wi-Fi 6E bands, respectively. The minimum gain achieved is 5 dBi in all possible configurations. A broadband rectifier circuit (4.67–7.0 GHz) with a staircase multistage transmission line matching network (MN) covering all resonant frequencies in various facet-loaded antenna configurations is proposed for RF-to-dc conversion purposes. The rectifier’s maximum power conversion efficiency (PCE) is achieved as 77.3% at a 13.5 dBm input power level, and the corresponding output voltage is 4.92 V.

In recent years, the enormous innovation in the wireless system has escalated the demands of fifth-Generation (5G) enabled RF Energy Harvesting (RFEH) and Wireless Power Transfer (WPT) systems. With this motivation, the proposed work introduces two efficient rectifier configurations for potential implementation in both RFEH and WPT systems covering global Sub-6 GHz 5G bands. The Design-1 presents a single-band rectifier covering 3.3-3.7 GHz sub-6 GHz 5G band. A dual Transmission Line (TL) based Matching Network (MN) is used to improve the rectifier performance. At 0 dBm, Design-1 achieved maximum Power Conversion Efficiency (PCE) of 76 % at 3.5 GHz and 4k & omega; load. The Design-2 presents a 3.3-5 GHz broadband rectifier circuit that covers the entire sub-6 GHz 5G bands. A MN based on multi-stepped TL is used to improve the rectifier performance for the broad frequency band and achieved a PCE greater than 35 % and 50 % at 0 and 9 dBm, respectively at a load value of 1k & omega;. For validation, prototypes of both rectifiers are fabricated and a very good agreement between simulated and measured results is achieved. The proposed rectifier configurations hold immense potential for implementation across nations and offer a global solution to self-sustainable low-powered 5G battery-less devices.

Low-power wireless sensors will play a big role in smart city applications. These sensors require a power supply to function. Batteries are not optimal for such numerous sensor networks because of their limited life and need for regular maintenance; hence, they are not a universal solution. RF energy harvesting (RFEH) and wireless power transfer (WPT) techniques have the potential to be a green and sustainable solution for supplying power to various low-power devices by capturing ambient RF energy. The ubiquitous nature of RF energy makes it available to exploit and reutilize in power wireless sensor nodes, wireless body area networks, wireless charging systems, RFID tags, and the Internet of Things [1] , [2] . Figure 1(a) displays a conceptual diagram of an RFEH/WPT system. To capture power from free space that is transmitted by the base station, the harvesting node needs a receiving antenna and rectifier to convert the power into dc signals. This dc output is then further utilized to feed a low-power device. Figure 1(b) shows that at 10-m distance from the cellular tower, a digital batteryless watch was powered by a rectenna operating at 1.8 GHz. This LCD watch (low-power device) required 1.5 V to function and was successfully powered up using the RFEH system [3] .

RF-based wireless energy harvesting (WEH) and wireless power transfer (WPT) are gaining attention due to their capability of powering various sensors and devices. A low-power device can be fed wirelessly by capturing ambient RF energy through a WEH system. In the case of a high-power device, a WPT system can provide the required amount of power using intentional RF sources.

A smart city necessitates spectrum and energy efficiency with increasing applications which demand an increasing number of nodes in the Internet of Things (IoT) system networks. In recent years, radio frequency (RF) energy harvesting is best suited to enhance the energy efficiency required for self-sustained IoT networks incorporated in smart cities. This work proposes a rectangular dielectric resonator antenna (RDRA), that comprises a rectangular dielectric resonator (DR) and slots loaded ground plane. The proposed antenna operates efficiently at 3.5 and 5.8 GHz frequencies and also achieves circularly polarized characteristics at two operating bands. A microstrip feeding approach opts for excitation of the proposed antenna. The radiational properties of the proposed antenna show that the antenna is suitable to operate for radio frequency energy harvesting in smart city applications efficiently. An HSMS2860 Schottky diode has been chosen for the rectification at two bands of frequencies. A proper impedance matching is achieved using microstrip transmission lines and rectangular stubs connected to the rectifier circuit. The proposed rectifier circuit offers the maximum power conversion efficiency (PCE) of 54.53% and 41.26% at 3.5 and 5.8 GHz frequencies respectively for 5 dBm input power. The output voltages obtained at two frequencies are 1.31 V and 1.16 V, respectively.

This article proposes a single band circularly polarized (CP) rectenna operate at a 2.45 GHz Wi-Fi band, using a hexagonal shape of a microstrip radiator and a voltage doubler rectifier for smart city applications. A partial ground plane embedded with isosceles triangular slot and notch helps in obtaining the desired resonance characteristics with improved antenna performance and reasonable miniaturization. Two crossed-slots, introduced into the radiating patch, yield CP characteristics. Also, the proposed antenna shows an omnidirectional radiational behavior that helps in harvesting RF energy from all of its surroundings. A voltage doubler configuration using the SMS7630-005 LF diode is chosen for designing a rectifier circuit to achieve a maximum conversion efficiency of 65.1% and an output voltage of 1.65 V at an input power of 0 dBm for the load resistance value of 4.1 kΩ which is very much suitable for powering low power sensing devices.

Rectifier is a fundamental element of a rectenna system that converts RF energy to direct current (dc). We proposed a triple-band rectifier using a novel matching technique and single series diode topology. First, we designed a single band rectifier and then converted it into a dual- and triple-band rectifier by introducing an appropriate transmission line and shorted stub, respectively, to convert simultaneously multiple RF signals into dc. The proposed rectifier operates at the popular frequency bands of 1.95, 2.7, and 5.8 GHz with power conversion efficiency (PCE) of 65.5%, 62%, and 57.1%, respectively, using a single impedance matching circuit.

This article describes a circularly polarized (CP) broadband rectenna enabling sensing nodes connected in the smart cities to harvest radio frequency (RF) energy from the surrounding atmosphere. The proposed antenna efficiently operates at the 5.8 GHz Wi-Fi band (5.725–5.875 GHz) and the Wi-Fi 6E band (5.925–7.125). The antenna is a semi-cylindrical dielectric resonator antenna (S-CDRA) energized by a microstrip feed. Semi-annular slots are introduced around a Bow-tie slot from the ground plane side, enhancing the bandwidth, gain, and CP characteristics. The antenna provides an impedance bandwidth (BW) of 2.89 GHz (5.45–8.34 GHz) and offers CP characteristics with an axial ratio (AR) bandwidth of 680 MHz (5.67–6.35 GHz). The antenna maintains a minimum gain of 4.8 dBic. A series-pair configuration is proposed for an extended operating range and better conversion efficiency. The maximum simulated and measured conversion efficiencies are 66.6% and 65.2% at 11 dBm input power, respectively.

Radio frequency (RF) energy harvesting is the most adopted technique for replacing conventional batteries. However, the available RF energy in the surrounding atmosphere is low and unstable, so the antenna with high gain and polarization-insensitive characteristics is desired to collect a massive amount of power from the low-density environment. A 90° twisted quarter sectored circularly polarized and high gain dielectric resonator antenna (DRA) operating within the 5.8 GHz Wi-Fi band, is investigated first time of its kind in this letter. A circular-shaped aperture coupled feeding approach is investigated for energizing the proposed antenna. A metallic strip is placed on the right face of the optimized DRA for creating circular polarization characteristics. The optimized antenna (0.67 λ×0.67 λ×0.029 λ) offers a gain value of 7.02 dBc at 5.8 GHz frequency. A shunt-diode rectifier circuit is implemented for rectification purposes. The power conversion efficiency achieved at the operating frequency is 72.5% for an input power level of 5.75 dBm.

This work presents a dual-polarized dielectric resonator antenna (DRA) operating over two frequency bands that cover LTE1800 and LTE2500 bands for radio frequency energy harvesting (RFEH) applications. An Eccostock HIK K10 material with a dielectric constant of 10 is used to create a DRA. The dimension of DRA is 9×16.1×5.5 mm 3 placed over the 1.6 mm thick FR4 substrate (ε r =4.4). The area of the substrate material is optimized as 60×50 mm 2 . A Bow-tie-shaped slot is created into the ground plane to help bring down the resonant frequency to 1.95 GHz and also helps in increasing the reflection coefficient performance. One more resonance is observed by placing a reflecting plane having an equal dimension to the antenna substrate at a gap of 20 mm from the antenna ground plane. In addition to this, an improvement in the antenna gain is also observed with a reflecting surface. The reflecting plane helps to increase the gain value. The maximum possible gain value is 8.36 dB at 2.6 GHz frequency. The proposed antenna exhibits omnidirectional radiation properties, thus it is suitable to harvest ambient EM energies available at LTE bands.