The wireless transfer of electromagnetic energy into the human body could power medical devices and enable new ways to treat various disorders. To control energy transfer, metal structures are used to generate and manipulate radio-frequency electromagnetic fields. Most systems for transfer across the biological tissue operate in the quasi-static limit, but operation beyond this regime could afford new powering capabilities. This review discusses some recent developments in the design and implementation of systems operating in the electromagnetic midfield, where transfer exploits wave-like fields in the body.

A novel compact wideband b andpass filter using rotational symmetric loaded structure is proposed in this paper. A λ/4 parallel coupled line is first introduced to form a passband with desired center frequency. The rotational symmetric structure with short/open circuit stubs is then introduced as a loading structure to improve the filter's performance. The rotational symmetric loading structure is discussed in detail in this paper, and a pair of transmission zeros is obtained and located at two sides of the passband to improve the passband selectivity intensively. Moreover, three open circuit stubs are utilized to replace one single stub for obtaining a wide stopband. At last, the proposed filter is fabricated and measured, and the results show a good agreement with each other.

The prediction of Radar Cross Section (RCS) of complex targets which present shadowing effects is an interesting challenge. This paper deals with the problem of shadowing effects in the computation of electromagnetic scattering by a complex target using Iterative Physical Optics (IPO). The original IPO is limited to cavities applications, but a generalized IPO can be applied to arbitrary geometries. This paper proposes a comparison between the classical PO approach and a physical approach based on shadow radiation (around forward direction) with PO approximation for the consideration of shadowing effects in generalized IPO. Based on the integral equations, a rigorous demonstration of this physical shadowing is provided. Then simulation results illustrate the interest of using physical shadowing both from the transmitter and towards the receiver, compared to the classical approach.

In this paper, a new design of asymmetric coplanar strip (ACS)-fed UWB planar monopole antenna with dual band-notched characteristics is presented and investigated. The proposed antenna is composed of an asymmetric ground plane, a semi-circular radiator, together with two open-ended half wavelength bow-shaped slots etched on the radiation patch. This leads to the desired dual notched bands of 3.12-3.69 GHz for WiMAX and 5.51-6.01 GHz for WLAN. Experimental results show that the designed antenna, with compact size of 29.5×12 mm², has stable and omnidirectional radiation pattern, sharp reduction in gain and group delay at notched frequencies. The very simple feeding structure and compact uniplanar design make it easy to be integrated within the portable device for UWB communication systems.

A novel single layer, coaxial probe feed compact triple band slotted microstrip patch antenna with modified ground plane for wireless application has been designed and analyzed. The presented antenna, occupying a compact size of 24×22×1.6 mm³, embodies a rectangular slotted patch and a rectangular ground plane modified with open ended step graded slots. The step graded slots are introduced on the ground plane to reduce the size of the antenna by reducing the resonant frequency and also to improve the operating bandwidth of the proposed antenna. The size of the antenna has been reduced by 74% by introducing slots on the ground plane. The measured bandwidths for -10 dB reflection coefficient are 360 MHz (1.72-2.08 GHz) at lower band, 300 MHz (3.36-3.66 GHz) at middle band and 3650 MHz (4.85-8.5 GHz) at upper band which cover the bandwidth requirements of 1.92 GHz PCS, 1.9 GHz PHS, 3.5/5.5 GHz WiMAX, 5.2/5.8 GHz WLAN, 5.2 GHz HisWaNa, 5.5 GHz Wi-Fi 802.11n and 5 GHz HiPERLAN wireless application bands.

An extremely simple design of a planar Fabry-Pérot cavity antenna is proposed as a very promising candidate for millimeter-wave wireless systems. The simplicity of this design is obtained by using a dielectric slab, here quartz, to form a single-layer cavity with thin layers of copper etched/printed on both sides, to form the ground plane on one side and the frequency-selective surface (FSS) on the opposite side of the slab. By keeping the planarity of the structure and not-requiring an additional supporting layer, the cavity is excited using an integrated feeding-slot antenna etched on its ground plane. The variations in the radiation properties of the proposed antenna, linked to its leaky-wave behavioral explanation, are studied by designing three prototypes with different maximum gain values. The prototype FPCs are designed to operate for Q-band wireless communication systems (here, resonating at three different frequencies in the range of 42-46 GHz). The performance of the designed antennas, backed by initial analytical and numerical simulations, is verified with a full set of measurement results.

Feed-forward artificial neural networks (ANNs) can provide the adequate model required for the linearization of power amplifiers (PAs) used in wireless communication systems. A common characteristic of previously available ANN-based models for linearization purposes is the use of a single real-valued ANN having two outputs. The contribution of this work is to report the benefits of performing such behavioral modeling based on two independent real-valued ANNs, where each network has a unique output. The proposed ANN-based model is applied to the behavioral modeling of a GaN HEMT class AB PA, and its accuracy is compared to previous approaches in two different scenarios. First, in case of similar number of network parameters, it is observed that the proposed ANN-based model can reduce the normalized mean-square error (NMSE) by up to 1.3 dB. Second, in a situation of comparable modeling accuracy (NMSE = -40 dB), it is observed that the proposed ANN-based model can reduce the number of network parameters by up to 40% (from 62 to 38 real-valued parameters).

A modified generalized memory polynomial model (MGMP) is proposed for RF power amplifiers (PAs). The MGMP model is derived by applying complexity-reduced technique to the generalized memory polynomial model (GMP)， and the least square (LS) algorithm is used for coefficient extraction. The proposed MGMP model is assessed using a GaN Class-F PA driven by two modulated signals (a WCDMA 1001 signal and a single carrier 16 QAM signal with 20 MHz bandwidth). The experimental results demonstrate that the MGMP model outperforms the memory polynomial (MP) model and the generalized memory polynomial (GMP) model. Compared with MP model, the MGMP model shows a normalized mean square error (NMSE) improvement of 2.13 dB in forward modeling, average adjacent channel power ratio (ACPR) improvement of 2.62/2.11 dB in the DPD application with almost identical number of model coefficients. In contrast with the GMP model, the MGMP model can achieve comparable forward modeling and linearization performance results, but reduces approximately 40% of coefficients.

A tunable metasurface composed of multiple resonant units is proposed, with each unit containing a block of SrTiO₃ ferroelectric and a periodical copper-wire structure. The local transmission coefficient of the metasurface is controlled by voltagetuning the permittivity of SrTiO₃ in each resonant unit. The function of this tunable metasurface is demonstrated by simulating beam steering at the angles of 30˚ and 14.47˚, respectively; as well as beam focusing at the focal lengths of 2λ₀ and 4λ₀, respectively.

In this paper, a novel compact dual-band microstrip antenna operating at two different bands namely C-band and X-band is presented and analyzed. The dual ultra wide band is realized by cutting two triangular slots on the right and on the left sides of the patch and a rectangular slot on the top side of the patch. The antenna structure is optimized and simulated using commercial software. The excitation is launched through a 50 Ohms microstrip line. According to simulation and measured results the proposed antenna can provide two separated impedance bandwidths of 500 MHz centered at 7 GHz and 2 GHz centered at 10.7 GHz and stable radiation patterns.

A novel compact wideband inphase multilayer power divider based on slotline-to-microstrip coupling structure is presented in this paper. To improve the isolation between output ports, this power divider breaks the conventional half-wavelength slotline configuration and introduces a lumped resistor. A wideband bandpass filter integrated with the power divider is designed to allow the power divider to reject the undesired signals located in adjacent frequency channels. This filter consists of two E-shape units. In order to improve its performance at low frequency band, a lumped capacitor is bridged between the two E-shape units. As an example, a wideband power divider combining with a filter is designed and fabricated. The experimental results show that the proposed power divider has a low insertion loss, high isolation, good return losses at all ports, good amplitude and phase balance, as well as flat group delay over the wide frequency band from 3.5 GHz to 10 GHz. In addition, the width of upper stopband reaches up to 3.8 GHz (12.9 GHz-16.7 GHz) corresponding to attenuation more than 20 dB.

In this work, a planar monopole ultra-wideband (UWB) antenna with an L-shaped stub on the ground plane is proposed. The novel extended L-stub in conjunction with the UWB radiator achieves an ultra wideband impedance matching with a compact size. The proposed antenna is fabricated and measured showing an ultra wide operating frequency range from 2.3 to over 14 GHz (VSWR < 2) with a unidirectional gain from 3-6.5 dBi and efficiency from 70-85% within the UWB band from 3.1-10.6 GHz. The proposed antenna provides a new way to improve ultra wideband impedance matching other than the frequently used tapered microstrip feed line. It also provides a way to improve the lower frequency bandwidth of the antenna without increasing the antenna's physical size, which is the most common method to use.

An X-band ferrite-loaded half mode substrate integrated waveguide (HMSIW) phase shifter is proposed and fabricated in this paper. A full-height E-plane Yttrium Iron Garnet (YIG) ferrite slab is embedded in the HMSIW to construct the non-reciprocal phase shifter. With the application of a magnetic bias field on the ferrite slab, the phase of the ferrite-loaded HMSIW can be adjusted and controlled. For a magnetic bias field of 1800 Gauss, the insertion loss is less than 3.2 dB from 9.7 to 11.0 GHz. The return loss is better than 10 dB over the same frequency range. The largest differential phase shift can be up to 337°. This circuit is easily integrated with other planar components and also has the capability to handle medium power level.

A novel ortho-mode transducer (OMT) for dual-band dual-polarized communication systems is proposed in this letter. The OMT is loaded with five posts in reasonable positions of the waveguides and a shorted circuit piston in the branch waveguide. Compared with the septum loaded traditional one, the presented OMT is more flexible, simple and easy to fabricate. Both simulations and measurements indicate that the impedance bandwidths of VSWR<1.15 ranging from 6.50 to 7.20 GHz and 8.80 to 10.2 GHz can be obtained. The low insertion losses indicate that the presented OMT can be used in actual project. Moreover, good isolation performance between the two input ports in both bands are obtained because of the inherent existence of cross polarization.

A typical magnetic resonance coupling based wireless Electric Vehicle (EV) charging system consists of a transmitting coil at the charging station and a receiving coil in the vehicle. In order to maintain good energy transfer efficiency of the wireless charging system, the effect of the proximal metallic object in the vicinity of the receiving coil has been investigated. Both from the theoretical simulation and experimental measurement, it has been observed that the resonance based wireless energy transfer system is very sensitive to the nearby metallic objects, leading to significant deterioration in energy transfer efficiency. This effect on the energy transfer efficiency is also seen to be different for different physical spacing between the transmitting and receiving coils. It is also found that the operating resonant frequency for optimum energy transfer efficiency changes with the metallic object in close proximity to the receiving coil. The theoretically simulated results well agree with the experimental results. The analysis will provide future guidelines for designing an efficient resonance coupling based wireless charging system for EVs even in the presence of metallic objects.

The rigorous evaluation of the NRCS (Normalized Radar Cross Section) of an object above a one-dimensional sea surface (2D case) needs to numerically solve a set of discretized integral equations involving a large number of unknowns. Thus, the direct solution of the impedance matrix equation via LU decomposition becomes the most expensive step in the MoM (Method of Moments) procedure. So, in order to minimize the computation cost, the iterative domain decomposition method called EPILE (Extended Propagation-Inside-Layer Expansion) was used and then was combined with the FBSA (Forward-Backward with Spectral Acceleration) to calculate the local interactions on the rough sea surface. The resulting fast method is called EPILE+FBSA. In this paper, we take advantage of the rank-deficient nature of the coupling matrices, corresponding to the object-surface interactions, to further reduce the complexity of the method by using the ACA (Adaptive Cross Approximation). Thus, the coupling matrices are strongly compressed without a loss of accuracy and the memory requirement is then strongly reduced. For a cylinder above a rough sea surface, the results show the efficiency of the accelerated EPILE+FBSA+ACA method.

A simple microstrip circular disc antenna to excite circularly polarized radiation is presented. In a single-probe fed circular disc sector patch, the corners are further truncated to obtain circular polarization characteristics. The truncation helps to reduce the ground plane dimensions making the antenna more compact with overall dimensions of 50 mm x 50 mm x 1.6 mm. The lengths of truncation necessary to achieve circular polarization are mathematically expressed. The simulated and experimental results are compared and are found to be in good agreement. Axial ratio bandwidth of 1.3% is obtained. The overall size reduction is 55% in comparison with the original disc sector antenna. The antenna resonates in the UMTS 1900-2170 MHz band and can be employed for Mobile Communication applications.

Small ultra high frequency (UHF) radio frequency identification (RFID) tags of fragment-type structure can be designed for broadband operation and for versatile impedance matching to different chips. The fragment-type tag structure can be optimized by using genetic algorithm. In our design, multi-objective evolutionary algorithm based on decomposition combined with enhanced genetic operators (MOEA/D-GO) is used for optimization searching. The multiple objectives are defined in terms of power transmission coefficients for operation in multiple RFID bands and for impedance matching to several prevailing RFID chips. For demonstration, a fragmented tiny square UHF tag of dimensions of 5.5 mm * 5.5 mm is designed for multi-band operation over the 433 MHz, 869 MHz and 915 MHz RFID bands, and a fragmented round tiny RFID tag of radius of 4.5 mm is also designed for versatile connection to five prevailing RFID chips at 915 MHz. The tiny round versatile tag is tested by connecting two chips, the IMPIMJ Monza-4 chip (11-143j) and ALIEN Higgs-3 chip (27-195j), respectively. Effects of input impedance and adjunct fragments on versatility of the design are further discussed.

A dual-band capacitive coupled planar inverted F antenna is presented. The antenna operates in two bands centered around 1.5 GHz and 2.4 GHz with nearly omnidirectional radiation pattern in the entire operating band. It offers a peak gain of 2.4 dBi at 1.5 GHz and 7 dBi at 2.4 GHz with an average efficiency of 82%, 97% respectively. Effects of key design parameters such as the distance between feed strip and radiator patch, the dimensions of the feed strip on the input characteristics of the antenna and length of slot have been investigated and discussed. The antenna is compact and simple to fabricate. The antenna posses an overall dimension of 10×40×6 mm³ when fabricated on substrate of dielectric constant 4.4 and thickness 1.6 mm.

3D integration using through-silicon-vias (TSVs) is gaining considerable attention due to its superior packaging efficiency resulting in higher functionality, improved performance and a reduction in power consumption. In order to implement 3D chip designs with TSV technology, robust TSV electrical models are required. Specifically, due to the increase of signal speeds into the gigahertz (GHz) spectrum, a high frequency electrical characterization best describes TSV behavior. In this letter, 5x50 μm TSVs are manufactured using a via-mid integration scheme and characterized using S-Parameters up to 65 GHz. At 50 GHz, the measured attenuation constant is 0.35 dB/via with a time delay of 0.7 ps/via.