Wireless charging is a technology of transmitting power through an air gap to electrical devices for the purpose of energy replenishment. The recent progress in wireless charging techniques and development of commercial products have provided a promising alternative way to address the energy bottleneck of conventionally portable battery-powered devices. However, the incorporation of wireless charging into the existing wireless communication systems also brings along a series of challenging issues with regard to implementation, scheduling, and power management. In this paper, we present a comprehensive overview of wireless charging techniques, the developments in technical standards, and their recent advances in network applications. In particular, with regard to network applications, we review the static charger scheduling strategies, mobile charger dispatch strategies and wireless charger deployment strategies. Additionally, we discuss open issues and challenges in implementing wireless charging technologies. Finally, we envision some practical future network applications of wireless charging.

Wireless Charging Technologies: Fundamentals, Standards, and Network Applications

Resonance conditions for a substrate-superstrate printed antenna geometry which allow for large antenna gain are presented. Asymptotic formulas for gain, beamwidth, and bandwidth are given, and the bandwidth limitation of the method is discussed. The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles.

Gain enhancement methods for printed circuit antennas

This paper presents a novel broadband rectenna for ambient wireless energy harvesting over the frequency band from 1.8 to 2.5 GHz. First of all, the characteristics of the ambient radio-frequency energy are studied. The results are then used to aid the design of a new rectenna. A novel two-branch impedance matching circuit is introduced to enhance the performance and efficiency of the rectenna at a relatively low ambient input power level. A novel broadband dual-polarized cross-dipole antenna is proposed which has embedded harmonic rejection property and can reject the second and third harmonics to further improve the rectenna efficiency. The measured power sensitivity of this design is down to $- {\bf 35}\;{\bf dBm}$ and the conversion efficiency reaches 55% when the input power to the rectifier is $- {\bf 10}\;{\bf dBm}$ . It is demonstrated that the output power from the proposed rectenna is higher than the other published designs with a similar antenna size under the same ambient condition. The proposed broadband rectenna could be used to power many low-power electronic devices and sensors and found a range of potential applications.

A High-Efficiency Broadband Rectenna for Ambient Wireless Energy Harvesting

With the development of wireless communication technology, the need for bandwidth is increasing continuously, and the growing need makes wireless spectrum resources more and more scarce. Cognitive radio (CR) has been identified as a promising solution for the spectrum scarcity, and its core idea is the dynamic spectrum access. It can dynamically utilize the idle spectrum without affecting the rights of primary users, so that multiple services or users can share a part of the spectrum, thus achieving the goal of avoiding the high cost of spectrum resetting and improving the utilization of spectrum resources. In order to meet the critical requirements of the fifth generation (5G) mobile network, especially the Wider-Coverage , Massive-Capacity , Massive-Connectivity , and Low-Latency four application scenarios, the spectrum range used in 5G will be further expanded into the full spectrum era, possibly from 1 GHz to 100 GHz. In this paper, we conduct a comprehensive survey of CR technology and focus on the current significant research progress in the full spectrum sharing towards the four scenarios. In addition, the key enabling technologies that may be closely related to the study of 5G in the near future are presented in terms of full-duplex spectrum sensing, spectrum-database based spectrum sensing, auction based spectrum allocation, carrier aggregation based spectrum access. Subsequently, other issues that play a positive role for the development research and practical application of CR, such as common control channel, energy harvesting, non-orthogonal multiple access, and CR based aeronautical communication are discussed. The comprehensive overview provided by this survey is expected to help researchers develop CR technology in the field of 5G further.

Full Spectrum Sharing in Cognitive Radio Networks Toward 5G: A Survey

An air-filled substrate integrated waveguide (SIW) made of a multilayer printed circuit board process is proposed in this paper. It is of particular interest for millimeter-wave applications that generally require low cost and low-loss performance and excellent power-handling capability. This three-layered air-filled SIW allows for substantial loss reduction and power-handling capability enhancement. The top and bottom layers may make use of a low-cost standard substrate such as FR-4 on which baseband or digital circuits can be implemented so to obtain a very compact, high-performance, low-cost, and self-packaged millimeter-wave integrated system. Over Ka-band (U-band), it is shown that the air-filled SIW compared to its dielectric-filled counterparts based on Rogers substrates RT/Duroid 5880 and also 6002 reduces losses by a mean value of 0.068 dB/cm (0.098 dB/cm) and 0.104 dB/cm (0.152 dB/cm), increases average power-handling capability by 8 dB (6 dB) and 7.5 dB (5.7 dB), and quality factor by 2.7 (2.8) and 3.6 (3.8) times, respectively. The peak power-handling capability of the proposed structure is also studied. A wideband transition is presented to facilitate interconnects of the proposed air-filled SIW with dielectric-filled SIW. Design steps of this transition are detailed and its bandwidth limitation due to fabrication tolerances is theoretically examined and established. For validation purposes, a back-to-back transition operating over the Ka-band is fabricated. It achieves a return loss of better than 15 dB and an insertion loss of ${\hbox{0.6}} \pm {\hbox{0.2 dB}}$ ( ${\hbox{0.3}} \pm {\hbox{0.1}}~{\hbox{dB}}$ for the transition) from 27 to 40 GHz. Finally, two elementary circuits, namely, the T-junction and 90 $^{\circ}$ hybrid coupler based on the air-filled SIW, are also demonstrated.

Air-Filled Substrate Integrated Waveguide for Low-Loss and High Power-Handling Millimeter-Wave Substrate Integrated Circuits

A novel class of low-cost, small-footprint and high-gain antenna arrays is presented for W-band applications. A 4 × 4 antenna array is proposed and demonstrated using substrate-integrated waveguide (SIW) technology for the design of its feed network and longitudinal slots in the SIW top metallic surface to drive the array antenna elements. Dielectric cubes of low-permittivity material are placed on top of each 1 × 4 antenna array to increase the gain of the circular patch antenna elements. This new design is compared to a second 4 × 4 antenna array which, instead of dielectric cubes, uses vertically stacked Yagi-like parasitic director elements to increase the gain. Measured impedance bandwidths of the two 4 × 4 antenna arrays are about 7.5 GHz (94.2-101.8 GHz) at 18 ± 1 dB gain level, with radiation patterns and gains of the two arrays remaining nearly constant over this bandwidth. While the fabrication effort of the new array involving dielectric cubes is significantly reduced, its measured radiation efficiency of 81 percent is slightly lower compared to 90 percent of the Yagi-like design.

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Low-Cost and High-Efficient W-Band Substrate Integrated Waveguide Antenna Array Made of Printed Circuit Board Process

In this article, the design procedure of the winning WEH device in the IMS2012 Student Design Competition is presented. The designed WEH circuit is a rectenna consisting of a rectifier in voltage doubler structure and a folded dipole antenna. The design steps of the rectifier circuit and the antenna are explained in detail, and simulation and measurement results are shown.

Highly Efficient Compact Rectenna for Wireless Energy Harvesting Application

The concept of substrated integrated waveguide (SIW)-fed horn and antipodal linearly tapered slot antenna (ALTSA) are jointly used to design a low-cost, high-gain, and efficient planar dielectric-loaded antenna for ultra-wideband gigabyte wireless services, which are demonstrated over $E$ - and $W$ -bands. SIW is used to feed the proposed antenna. To increase the gain of the antenna, a dielectric-loaded slab is used in front of the antenna and works as a dielectric guiding structure. The SIW feed, the proposed antenna, and the loaded dielectric are all integrated in a planar single layer substrate, resulting in low cost and easy fabrication. Low-cost printed circuit board (PCB) process is utilized to fabricate the antenna structure with rectangular and elliptical shaped loaded dielectrics. Measured bandwidth of the antenna covers both $E$ - and $W$ -bands (70–110 GHz). Measured gain of the single-element antenna is ${\hbox{14}}\pm {\hbox{0.5}}$ dBi, while the measured radiation efficiency of 84.23% is obtained at 80 GHz. Wideband SIW power dividers are used to form a 1 $\,\times\,$ 4 array structure. Measured gain of the 1 $\,\times\,$ 4 array antenna is ${\hbox{19}}\pm {\hbox{1}}$ dBi, while the measured radiation pattern and gain are almost constant within the wide bandwidth of the antenna.

Planar High-Gain Dielectric-Loaded Antipodal Linearly Tapered Slot Antenna for $E$ - and $W$ -Band Gigabyte Point-to-Point Wireless Services

This letter presents a low-cost, high-gain, and high-efficiency 4 × 4 circular patch array antenna for gigabyte point-to-point wireless services at E-band (81-86 GHz). The antenna structure consists of two layers. The feed network is placed at the bottom layer, while the circular patches are on the top layer. To increase the efficiency of the antenna array, substrate integrated waveguide (SIW) is used to feed the circular patches through longitudinal slots etched on the top metallic surface. Low-cost printed circuit board (PCB) process is used to fabricate the antenna prototype. Simulated and measured bandwidths of the antenna array are 7.2%, which covers the desired frequency range of 81-86 GHz. Measured gain of the 4 × 4 antenna array is 18.5 dBi, which is almost constant within the antenna bandwidth. Measured radiation efficiency of 90.3% is obtained.

High-Efficient Patch Antenna Array for E-Band Gigabyte Point-to-Point Wireless Services

Due to the low atmospheric absorption over W-band, numerous applications are expected, which should be developed at low cost. Short wavelength makes the dimension of antennas in this frequency range small, which usually requires sophisticated and expensive fabrication process. This communication presents a class of integrated wideband pyramidal horn antennas which can be made of low-cost multilayered printed circuit board (PCB) process. The proposed horn antenna radiates along the broadside to the substrate and uses substrate integrated waveguide (SIW) as its feeder. Transverse slot on the top metallic surface at the end of SIW is deployed to drive the horn antenna. Metalized via holes are used to synthesize the horn walls. The opening of the horn antenna is discretely flared from the bottom to the top layer. Measured bandwidth of the antenna is 35 GHz (70-105 GHz) while a relatively constant gain of 10 ± 1 dB is obtained over most of the bandwidth.

N. Ghassemi

Papers

Low-Cost and High-Efficient W-Band Substrate Integrated Waveguide Antenna Array Made of Printed Circuit Board Process

Highly Efficient Compact Rectenna for Wireless Energy Harvesting Application

Planar High-Gain Dielectric-Loaded Antipodal Linearly Tapered Slot Antenna for $E$ - and $W$ -Band Gigabyte Point-to-Point Wireless Services

High-Efficient Patch Antenna Array for E-Band Gigabyte Point-to-Point Wireless Services

Millimeter-Wave Integrated Pyramidal Horn Antenna Made of Multilayer Printed Circuit Board (PCB) Process