Some microobjects can concentrate an incoming incident plane wave and create the socalled photonic nanojets. These highly focused emerging beams have a high intensity and can be used in applications such as microscopy, beam manipulation and imaging. In this article, it is shown that an adequate choice of geometric shape and material can lead to an improvement of the electric field enhancement capability of nanojets by a factor of 40%.

A coax-feed low profile dual-polarized circular patch antenna with ±45˚ polarization is presented. The antenna consists of a dual-polarized circular patch excited by two coax-lines and an AMC reflector. By using the AMC reflector as the ground plane of the patch antenna, the profile of the antenna is reduced to λ/8 of the operation frequency, which is much lower than that of the conventional dual-polarized patch antenna. The experimental results show that the proposed design obtains a wide bandwidth (2.12-2.77 GHz) and a high isolation (>35 dB) over the entire band. In addition, the front-back radio of the antenna is improved significantly by using the AMC reflector. The wide bandwidth, low-profile and high front-to-back ratio make the antenna a good candidate as a base station antenna for WLAN, WiMAX and LTE applications.

A dual-beam frequency scann ing microstrip antenna is proposed in this letter. The wellknown characteristic of the conventional leaky wave antenna is the beam scanning with operating frequency variation. Here, four slots are applied on the ground plane of the conventional leaky wave antenna structure to obtain the dual-beam frequency scanning characteristic. According the results, it shows that this work with relatively simple structure radiating not only in upper half-plane, but also in lower half-plane. The upper half-plane main lobe scans from 356˚ (-4˚) to 24˚ (scanning region is 28˚). Meanwhile, the lower half-plane main lobe scans form 190˚ (-170˚) to 161˚ (scanning region is 29˚). The 7-dB return loss bandwidth is 600 MHz from 3.4 GHz to 4 GHz. In addition, the measured average antenna gain is about 5.3 dBi in the operating frequency.

Wireless power transmision has been analytically studied in near-field coupling systems based on the small-antenna and near-field approximations, and in microwave power beaming systems based on the far-field approximation. This paper attempts to provide a general solution based on full-wave analysis to wireless power transmission between two circular loops. The solution applies to arbitrary transmit and receive loop radii, transmission range, orientation and alignment of the loops, and dielectric properties in a homogeneous isotropic medium. The power link is modeled as a two-port network and the efficiency based on simultaneous conjugate matching is used as the performance metric. The self and mutual admittances are analytically solved by expressing the current on the loops in Fourier series and the fields in vector spherical wave functions, and by the use of vector addition theorem to relate the coupling between the loops. The general solution is then applied to draw new insights such as the optimal carrier frequency between symmetric loops and impact of higher order modes on the power transfer efficiency between asymmetric loops.

It is well known tha the conventional edge element method in solving vector Maxwell's eigenvalue problem will lead to the presence of nonphysical zero eigenvalues. This paper uses the mixed finite element method to suppress the presence of these nonphysical zero eigenvalues for 2D vector Maxwell's eigenvalue problem in anisotropic media. We introduce a Lagrangian multiplier to deal with the constraint of divergence-free condition. Our method is based on employing the first-order edge element basis functions to expand the electric field and linear nodal element basis functions to expand the Lagrangian multiplier. Our numerical experiments show that this method can successfully remove all nonphysical zero and nonzero eigenvalues. We verify that when the cavity has a connected perfect electric boundary, then there is no physical zero eigenvalue. Otherwise, the number of physical zero eigenvalues is one less than the number of disconnected perfect electric boundaries.

By the transfer matrix approach we numerically study the electromagnetic properties (narrow peak positions) of the transmission spectra for microspheres coated by a multilayered stack with the generalized Cantor structure (fractal). As opposed to the standard Cantor system with removed γ/3 [γ=1] section we consider here the solid stack with Si/SiO2 layers at general γ value. In such a solid composition the SiO2 layers replace the empty Cantor sections and the parameter γ acquires meaning of a specific control parameter. At successive generations the central layers (in blocks of the spherical stack) acquire a progressive decreased width that leads to generation of the radially inhomogeneous defects. We show that the wave phase interference in such a fractal pattern leads to formation of very narrow electromagnetic transmittance resonances that can be used in modern optoelectronics.

In this letter, a reflectarray antenna based on the folded stepped impedance resonator (SIR) patch-slot configuration with variable size is presented. A novel frequency selective surface (FSS) in the reflectarray as a ground plane for reducing radar cross section (RCS) level is applied. The FSS is based on the folded SIR configuration. Two prime-focus 15 × 15 reflectarray antennas backed on the folded SIR FSS ground and a conventional ground are designed and manufactured. The radiation performance of a reflectarray element backed either by a solid ground plane or a band-stop FSS structure is compared. The measured results demonstrate that the radiation pattern and gain of the FSS-backed reflectarray are almost same to its counterpart backed by a conventional ground plane at the operating band of 11.5 GHz. The RCS is effectively reduced in the out of this band when compared with the reflectarray with a solid metal ground plane of the same dimension.

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.