Low profile multiband rectenna for efficient energy harvesting at microwave frequencies

This paper presents the design and development of a multiband rectenna for ambient RF energy harvesting. The proposed rectifying antenna consists of fractal-based geometry to obtain GSM 0.9 GHz (0.8–1.2 GHz), GSM 1.8 GHz (1.6–2.1 GHz), WLAN 2.5 GHz (2.2–2.8 GHz), Wi-MAX 3.5 GHz (3.1–4.0 GHz), WLAN 5.5 GHz (5.3–6.4 GHz) and 7.35 GHz (7.0–7.8 GHz) resonating bands. The designed sensing antenna is low profile, lightweight and small in size with two circularly polarized bands at frequencies 1.8 and 2.5 GHz. In the proposed rectenna, a dual-stage voltage doubler rectifying circuit is utilized for converting surrounding RF signals into DC power. A matching network is connected between the fractal antenna and the rectifying circuitry for realizing a good impedance matching between them. To verify the proposed design, a prototype rectenna is fabricated and measured results are compared with the simulated results. The proposed rectifier provides an RF to DC conversion efficiency of 78%.     

Novel miniaturized folded UWB microstrip antenna‐based metamaterial for RF energy harvesting

This paper presents a design of an ultra‐wideband (UWB) cylindrical metamaterial (MTM) antenna for radio frequency (RF) energy harvesting to suit the fields of Internet of Things (IoT) applications. The patch circuitry is based on 3×5 Hilbert‐shaped MTM unit cells array to enhance the antenna bandwidth. While, the antenna ground plane is defected with an electromagnetic band gap structure to enhance the gain. The antenna is mounted on a polytetrafluoroethylene cylindrical substrate of an outer diameter of 15 mm and length of 32 mm with 1 mm in thickness. The substrate relative permittivity is 2.04, and the loss tangent is 0.0002. The antenna patch and the ground plane structures are printed with silver nanoparticles ink using a ^2.5D CNC plotter machine. The fabricated prototype provides an UWB over the frequency range from 3.77 up to 13.89 GHz with a first separate resonant mode at 3 GHz. The antenna performance is tested numerically using two different software packages of CST MWS and HFSS. Then, an experimental validation is conducted to realize the performance of the proposed antenna in harvesting the RF energy. Excellent conversion efficiency, about 90%, is achieved at 5.8 GHz. Finally, the antenna radiation patterns and S₁₁ spectrum are measured and compared against their simulated results to achieve good agreements.     

基于压电材料的双频段混合能量收集天线

针对环境混合能量收集(天线)的小型化设计目标,设计一种基于聚偏氟乙烯(PVDF)压电材料的双频段共面波导(CPW)天线。天线的主要辐射单元为矩形铜皮贴纸,两侧对称的L型铜皮贴纸形成共面波导馈电结构,并作为微扰单元改变天线的表面电流分布,实现双频的设计要求。天线设计并制造在PVDF压电薄膜上,由于压电材料本身所具备的压电特性和高介电常数,该天线可同时收集射频与振动2种能量,天线尺寸得到有效减小。实验结果表明：该天线可同时工作在2.4 GHz和5.8 GHz的常用工业、科学与医学(ISM)频段,峰值增益分别为0.77 dB和2.47 dB。     

一种基于缝隙结构的小型双频段射频能量接收天线

随着超低功耗芯片技术的发展,无线传感器节点的功耗已进入微瓦（μW）级范围,使低功耗传感器利用周围环境中的射频无线能量为自身供电成为可能。提出了一种用于无线传感器节点的小型射频能量接收天线。该天线采用微带缝隙结构,基于缝隙天线设计理论,应用全波电磁场工具对其进行了设计及仿真优化,并获得了该结构谐振点随尺寸变化的一般规律。在常用FR4材料的小尺寸双面PCB板上,通过开槽加载和微带线馈电方法使天线可以同时工作在GSM和ISM两个频段。在1．9GHz和2．4CHz频率点上,天线的回波损耗分别为-39．4dB和-20．8dB,最大增益分别达到1．4dBi和2．9dBi,测试与仿真结果基本吻合。该天线含地平面在内的尺寸为5cm×5cm,实现成本低,可同时接收两个频段的射频能量,有效地扩展了频率适应范围,提高了能量接收效率。     

Cognitive radio network with continuous energy‐harvesting

In this paper, the performance of a cooperative cognitive radio (CR) network is investigated under continuous energy harvesting scenario. A CR node harvests energy from both the sources: non‐radio frequency (RF) signal (ambient sources) or from RF signal (primary user signal). It harvests from non‐RF signal during sensing time of its detection cycle, and from both the sources, RF signal and non‐RF signal, during transmission time as per sensing decision. Several novel analytical expressions are developed to indicate the harvested energy, energy reward, energy cost in a detection frame, and throughput. The performance of the CR network is investigated to maximize the throughput considering energy causality constraints and collision constraints. Analytical results are validated through extensive simulation results. Copyright © 2016 John Wiley & Sons, Ltd.     

A reconfigurable wideband MIMO antenna combines RF energy harvesting

This article introduces a novel and groundbreaking approach combining multiple-input-multiple-output (MIMO) technology with radio frequency (RF) energy harvesting. The proposed antenna consists of two semi-circular monopole antenna components, optimized with dimensions of 89 × 51.02 × 1.6 mm³, that share a common ground plane to achieve MIMO characteristics. A series of split-ring resonators on the ground plane significantly enhances the isolation between the two radiating components. Band-notched features are performed in the 3.5 GHz WiMAX and 5.5 GHz WLAN bands through modified C-shaped slots in the radiating patch and two rectangular split-ring resonators serving as parasitic devices near the feed line. The reconfiguration of band-notching is made possible by controlling the modes of the embedded PIN diodes. The two antenna elements maintain mutual coupling below −18 dB from 1.5–13 GHz, achieving an impressive 158.62% impedance bandwidth. The antenna's efficiency and gain experience significant drop, indicating effective interference suppression at the center frequencies of the notch bands, and its performance in MIMO systems is assessed through parameters including envelope correlation coefficient, port isolation, radiation patterns, efficiency, gain, and diversity gain. The simulated properties of the designed antenna closely align with the measured outcomes, demonstrating its reliability and consistency. Moreover, the article evaluates the antenna's potential for RF energy harvesting, achieving a maximum harvested energy of 4.88 V. This proposed antenna can be used in multiple applications, like wideband, band-notching MIMO, and RF energy harvesting. This proposed antenna is an efficient, reconfigurable wideband MIMO antenna with novel RF energy harvesting capability.     

Slot-array antennas fed by coplanar waveguide for millimeter-waveradiation

Slot-array antennas with parasitic slots, slot-array antennas fed by coplanar waveguide (CPW), and two-dimensional slot-array antennas fed by CPW were fabricated on fused quartz substrates, and the receiving properties of the antennas were investigated at 94 GHz with the goal of increasing the power gain of the slot antennas. It was found that the power gain of the slot antenna could be increased by 11 dB over a single-slot antenna by using a two-dimensional (8×3) slot-array antenna fed by CPW. It was confirmed that the improvement of the power gain was caused by decreasing surface-wave power in the substrate and by sharpening antenna patterns perpendicular to the substrate     

A POMDP‐based long‐term transmission rate maximization for cognitive radio networks with wireless‐powered ambient backscatter

Wireless energy harvesting enables wireless‐powered communications to accommodate data services in a self‐sustainable manner over a long operational time. Along with energy harvesting, an ambient backscatter technique helps a secondary transmitter reflect existing radio frequency (RF) signal sources to communicate with a secondary receiver when the primary channel (PC) is utilized. However, secondary system performance is significantly affected by factors such as the availability of the primary channel, imperfect spectrum sensing, and energy‐constrained problems. Therefore, we propose a novel approach for wireless‐powered cognitive radio networks (CRNs) to improve the transmission performance of secondary systems. To reduce the dependence of the secondary system on RF sources, in the paper, we provide a new paradigm by integrating ambient backscattering with both RF and non‐RF wireless‐powered communications to facilitate secondary communications. On the basis of the sensing result in a time slot, the secondary transmitter can dynamically select the operational action: (a) backscattering, (b) harvesting, or (c) transmitting to maximize the long‐term achievable data transmission rate at the secondary receiver. In addition, the optimal action set for CRNs with wireless‐powered ambient backscatter is selected by the partially observable Markov decision process (POMDP), which maximizes an expected transmission rate calculated over a number of subsequent time slots. The proposed scheme aims to improve long‐term transmission rate of CRNs with wireless‐powered ambient backscatter in comparison with conventional schemes where an action is taken only to maximize the immediate reward in every single time slot.     

Frequency Tunable Microstrip Patch Antenna Using RF MEMS Technology

A novel reconfigurable microstrip patch antenna is presented that is monolithically integrated with RF microelectromechanical systems (MEMS) capacitors for tuning the resonant frequency. Reconfigurability of the operating frequency of the microstrip patch antenna is achieved by loading it with a coplanar waveguide (CPW) stub on which variable MEMS capacitors are placed periodically. MEMS capacitors are implemented with surface micromachining technology, where a 1-mum thick aluminum structural layer is placed on a glass substrate with a capacitive gap of 1.5 mum. MEMS capacitors are electrostatically actuated with a low tuning voltage in the range of 0-11.9 V. The antenna resonant frequency can continuously be shifted from 16.05 GHz down to 15.75 GHz as the actuation voltage is increased from 0 to 11.9 V. These measurement results are in good agreement with the simulation results obtained with Ansoft HFSS. The radiation pattern is not affected from the bias voltage. This is the first monolithic frequency tunable microstrip patch antenna where a CPW stub loaded with MEMS capacitors is used as a variable load operating at low dc voltages     

Monolithic SiGe Up‐/Down‐Conversion Mixers with Active Baluns

The purpose of this paper is to describe the implementation of monolithically matching circuits, interface circuits, and RF core circuits to the same substrate. We designed and fabricated on‐chip 1 to 6 GHz up‐conversion and 1 to 8 GHz down‐conversion mixers using a 0.8 µm SiGe hetero‐junction bipolar transistor (HBT) process technology. To fabricate a SiGe HBT, we used a reduced pressure chemical vapor deposition (RPCVD) system to grow a base epitaxial layer, and we adopted local oxidation of silicon (LOCOS) isolation to separate the device terminals. An up‐conversion mixer was implemented on‐chip using an intermediate frequency (IF) matching circuit, local oscillator (LO)/radio frequency (RF) wideband matching circuits, LO/IF input balun circuits, and an RF output balun circuit. The measured results of the fabricated up‐conversion mixer show a positive power conversion gain from 1 to 6 GHz and a bandwidth of about 4.5 GHz. Also, the down‐conversion mixer was implemented on‐chip using LO/RF wideband matching circuits, LO/RF input balun circuits, and an IF output balun circuit. The measured results of the fabricated down‐conversion mixer show a positive power conversion gain from 1 to 8 GHz and a bandwidth of about 4.5 GHz.     

X‐Band Phased Array Antenna Using Ferroelectric (Ba,Sr)TiO3 Coplanar Waveguide Phase Shifter

A phased array antenna was fabricated using four‐element ferroelectric phase shifters with a coplanar waveguide (CPW) transmission line structure based on a Ba0.6Sr0.4TiO3(BST)/MgO structure. Epitaxial BST films were deposited on MgO (001) substrates by pulsed laser deposition. To attain the large differential phase shift and small losses for a ferroelectric CPW phase shifter, an impedance‐matching‐part adding technique between the effective transmission line and connecting cable was used. The return loss and insertion loss for this technique‐adapted BST CPW device were improved with respect to those for a normal BST CPW device. For an X‐band phased array antenna system consisting of ferroelectric BST CPW phase shifters, power divider, dc block, patch antenna, and programmed dc power, the steering beam could be tilted by 15° in either direction.     

Right‐Angle‐Bent CPW for the Application of the Driver‐Amplifier‐Integrated 40 Gbps TW‐EML Module

In this letter we present a right‐angle‐bent coplanar waveguide (CPW) which we developed for the application of the driver amplifier‐integrated (DAI) 40 Gbps traveling wave electroabsorption modulated laser module. The developed CPW realized parallel progression of the radio frequency (RF) and light using a dielectric overlay structure and wedge bonding on the bending section. The measured S₁₁ and S₂₁ of the developed CPW were kept below ?10 dB up to 35 GHz and ?3 dB up to 43 GHz, respectively. These measured results of the CPW were in good agreement with the simulation results and demonstrated the applicability of the CPW to the 40 Gbps communication module.     

Microwave measurement of coplanar-type resonator fabricated with YBCO film

High temperature superconducting (HTS) Y–Ba–Cu–O (YBCO) films were prepared on MgO polycrystal substrates by the sol–gel process. The temperature dependence of the surface resistance (R_s) of the YBCO film around 9.9 GHz was observed. YBCO coplanar waveguide (CPW) quarter-wavelength (λ/4) resonator operating around 2 GHz was fabricated using the sol–gel film, and RF properties of the YBCO CPW resonator was compared with that of normal metal resonator. The temperature and stored energy dependence of the transmission characteristics were observed in order to examine the temperature and power handling capabilities of the HTS resonator. The quality factor (Q₀) of the YBCO CPW λ/4 resonator increased significantly as the stored energy decreased, whereas the resonant frequency hardly changed. Moreover, the magnetic penetration depth at 0 K (λ₀) was also estimated.     

环境射频能量收集技术的研究进展及应用

随着超低功耗集成电路技术的发展,电子微系统的功耗已进入微瓦（μW）级范围,使其利用周围环境中的射频能量为自身供电成为可能。在回顾无线能量传输的历史以及介绍环境射频能量收集的可行性及其应用研究成果和进展的基础上,分析环境射频能量收集在超低功耗电子微系统中广泛应用所面临的关键技术、难点以及可能的解决方法;最后讨论了环境射频能量收集技术的发展方向,使该领域有待于研究的问题和方向更加具体化、明确化。     

Compact CPW-Fed ultrawideband MIMO antenna using hexagonal ring monopole antenna elements

In this paper, a compact coplanar waveguide (CPW) fed ultra-wide band (UWB) multi input multi output (MIMO) antenna is proposed. The antenna consists of two antiparallel hexagonal ring monopole elements. Circular arcs shaped grounded stubs are used to enhance the isolation, both the arcs are connected through stub to make common ground. Tapering of the slots of CPW feed line at feed point, and grounded slots are introduced for impedance matching over UWB. The proposed antenna is fabricated and impedance bandwidth, isolation, radiation pattern, and gain are measured. Moreover, envelop correlation coefficient (ECC) results are given. Proposed antenna structure operates in the frequency range 3–12 GHz with a fractional bandwidth of 120% keeping isolation better than 15 dB. The antenna has a compact size of 45 × 25 mm².     

Design of UWB monopole antenna with dual notched band characteristics by using π-shaped slot and EBG resonator

In this paper, we propose the design of coplanar waveguide (CPW) ultra-wideband (UWB) dual notched band monopole antenna with a π-shaped slot and EBG is proposed. The designed antenna produces an impedance bandwidth of 2.7–11.7 GHz (VSWR < 2), except with 3.4 GHz (3.3–3.7 GHz) for S-band WiMAX application and 6.9 GHz (6.5–7.2 GHz) for C-band IEEE INSAT applications. Here, the lower and upper notches are realized by proposing a π-shaped slot on the radiating element and an electromagnetic bandgap structure as a resonator integrated on either side of the ground plane. Meanwhile, the impedance over a frequency range and current distribution are also plotted for the proposed design. The antenna prototype is fabricated and characterized experimentally for validation purpose. Fair matching is observed among the simulated and measured results.     

CPW-fed folded-slot antenna for 5.8 GHz RFID tags

A coplanar waveguide (CPW)-fed capacitive folded-slot antenna is proposed for the radio frequency identification (RFID) application at 5.8 GHz. The antenna is fabricated on a 30/spl times/30 mm substrate. The measured bandwidth and antenna gain are 7.5% and 4.2 dBi, respectively. Radiation patterns are almost omnidirectional in the H-plane. These properties and the compact and uniplanar structure make the antennas suitable for use as RFID tags.     

Piezoelectrically actuated RF MEMS DC contact switches with low voltage operation

In this paper, fully integrated radio frequency (RF) microelectromechanical system (MEMS) switches with piezoelectric actuation have been proposed, designed, fabricated, and characterized. At a very low operation voltage of 2.5V, reliable and reproducible operation of the fabricated switch was obtained. The proposed RF MEMS switch is comprised of a piezoelectric cantilever actuator with a floated contact electrode and isolated CPW transmission line suspended above the silicon substrate. The measured insertion loss and isolation of the fabricated piezoelectric switch are -0.22 dB and -42dB at a frequency of 2GHz, respectively.     

Broadband electronically tunable planar active radiating elementsand spatial power combiners using notch antennas

A Gunn device has been integrated with two types of active planar notch antennas. The first types uses a coplanar waveguide (CPW) resonator an a stepped-notched antenna with bias tuning to achieve a bandwidth of 275 MHz centered at 9.33 GHz with a power output of 14.2±1.5 dBm. The second type uses a CPW resonator with a varactor for frequency tuning to achieve a bandwidth of over 1.3 GHz centered at 9.6 GHz with a power output of 14.5±0.8 dBm. This is equivalent to over 14% electronic tuning bandwidth. Both configurations exhibit a very clean and stable output signal. A theoretical circuit model was developed to facilitate the design. The model agrees well with experimental results. Injection-locking experiments on the second configuration show a locking gain of 30 dB with a locking bandwidth of 30 MHz at 10.2 GHz. Power combining experiments of two-varactor-tuned CPW active notch antenna elements in a broadside configuration have achieved well over 70% combining efficiency throughout the wide tuning range. The circuits have advantages of small size, low cost, and excellent performance     

Miniature high gain slot-fed rectangular dielectric resonator antenna for IoT RF energy harvesting

Radio-frequency (RF) energy harvesting is a promising candidate for alternative power source that can reduce the dependencies on batteries. However, its power density is very low which makes it crucial to have a high gain antenna to increase the power received by the system. This study presents the design of miniature high gain dielectric resonator antenna for RF energy harvesting application with high figure of merit to increase the power received. Numerical approximation is used to assist the antenna design and modelling. The design focused on three parameters which are the width, length, and height of the dielectric resonator. The performance, electric field density, and the radiation patterns of the dielectric resonator antenna have been observed by varying the design parameters. The effect of air gap to the performance is investigated and it is found that 8.11–13% gain improvement and up to 36% improvement in impedance matching is achieved through incorporating thin air gap between the dielectric resonator. Soda-lime glass with relative permittivity 7.75 is used which allows miniaturization and transparency. Experimental results show reasonable agreement to the simulations. The work shows highest antenna gain with smallest size with high FOM at 5 GHz ISM band compared to previous works.