A dual-band flexible antenna incorporated with the fractal structure using coplanar waveguide (CPW) is proposed for 2.42 GHz WLAN and 3.78 GHz WiMAX applications. The antenna is printed on a low-cost FR4 substrate having a thickness of 0.5 mm with overall antenna dimension of 97.48x80 mm². Incorporation of fractal geometry leads to improvement in terms of impedance bandwidth and radiation efficiency. The simulated and measured results of the proposed antenna in terms of return loss (S₁₁), gain, radiation pattern, and VSWR are presented here which show great correlation. The measured impedance bandwidth and gain of the flexible antenna are 17.08% (2.20 GHz-2.61 GHz), 16.30% (3.38 GHz-3.98 GHz), 4.56 dBi and 1.09 dBi, respectively. The proposed dual-band antenna shows omnidirectional and bidirectional radiation patterns in H and E-planes which makes it suitable for its use in low-cost Bluetooth/WLAN/WPAN/WiMAX applications.

Conical and cylindrical dielectric resonator elements are vertically stacked and excited by a simple coaxial monopole. Compared to all earlier configurations, the proposed geometry significantly improves the impedance bandwidth. The ultrawideband response is enhanced due to the multiple resonances occurring by the suggested hybrid antenna. The footprint area of the antenna is only 63.6 mm² or 25.44 x10^-3λ_o ² at the lowest operating frequency. The performance of the antenna is verified experimentally and numerically. Presented results show that the proposed hybrid monopole-DRA has a measured impedance bandwidth up to 148.6% (S₁₁ < -10 dB) along with consistent monopole-like radiation patterns and peak gain of 7.14 dBi. With such properties, the proposed hybrid monopole-DRA can be used in different ultra-wideband wireless applications and as wideband electromagnetic interference (EMI) sensors.

Compressive sensing for through-wall radar imaging (TWRI) is a promising method to obtain a high-resolution image with limited number of measurements. The capability of the existing method in the framework of CS is limited due to the model error stemmed from the approximated signal model which does not consider multipath returns or only consider first-order interior wall multipath returns. In order to exploit various multipath returns, finite-difference time domain (FDTD) technique is used to obtain the scattered signal for each assumed target position and then to construct the exact forward scattering model. Then, sparse reconstruction is used to solve this linear inverse problem. Numerical results demonstrate that the proposed approach performs better at ghost suppression in the same condition of the signal-to-noise ratio (SNR).

This paper proposes a new two-stage channel estimation (TSCE) method to estimate the cascaded channels in amplify-and-forward (AF) one-way relay network (OWRN) with multiple transmit and receive antennas. Different from the existing estimation methods, the proposed TSCE estimates the cascaded channel matrix by utilizing the special structure of the received signal in the destination and by exploiting the correlations among the cascaded channel matrix entries. The TSCE not only obtains the channel state information (CSI) when receiving training sequences, but also improves the accuracy of CSI when receiving the data sequences. Simulation results demonstrate that the proposed TSCE can improve estimation accuracy compared with traditional channel estimation schemes.

A low-profile dual tuning stub loaded microstrip line-fed multi-slot antenna is presented in this paper, which covers most of the significant 4G LTE bands from 850 MHz to 2800 MHz and beyond. The slot antenna consists of three wide slot sections: two orthogonal slots and a circular slot at the junction of those two slots. This multi-slot antenna is excited by a microstrip feed line loaded with dual stubs, which is on the other side of the dielectric substrate. The stubs are terminated across the width of orthogonal slots. Two of these slots along with feed lines are placed on two corners of the ground plane for pattern diversity. Numerical simulation and measurement results on a fabricated prototype demonstrate excellent agreement in scattering parameters. Good port isolation and gains are also obtained. This design is suitable for use in LTE mobile terminals.

A new coplanar waveguide (CPW) fed ultra-wideband (UWB) antenna with band notched characteristic is proposed in this paper. In order to achieve sharp and controllable notch-band characteristic, one pair of half-wave-length stubs and slits is introduced inside the tapered slot and circular patch, respectively, on the basis of a UWB antenna. Simulated and measured results show that the antenna has a reflection coefficient (S₁₁) less than -10 dB in the range of 3.0 to 11 GHz, which can meet the requirements of a UWB communication system. It shows a good notch characteristic in 5.0~5.8 GHz, which can covers the operating band of wireless local area network (WLAN) well. The antenna has a stable gain and good radiation characteristics in the pass band. It is simple in structure and easy in fabrication. Moreover, it has broad application prospects.

This work describes the fabrication and characterization of a frequency reconfigurable patch antenna using ferrofluid actuation. The reconfiguration is based on a variation of dielectric constant of the substrate. For this, the substrate is modified by placing channels in it filled with ferrofluid and isopropanol-water solution. The relative position of ferrofluid along the channels is controlled by an external magnetic field which results in a relocatable spatial difference in the dielectric constant value. The targeted reconfigurability with stable radiation characteristics at the accessible frequencies is validated through antenna reflection loss and radiation pattern measurements. Additionally, actuation speed of the fluid immerged in the polar mixture is measured by sequential image analysis.

There exist some problems that the water content of the test object cannot be reflected in real time. The detection time is too long, and the heating measurement method destroys the seed tissue for the traditional measurement of the water content of the seed. In this paper, a structure of single excitation coil to double receiving coils is proposed to measure the water content of the seed via electromagnetic induction. The relative permittivity of the seed can be obtained by the relationship between the amplitude ratio and the water content of the seed. First of all, according to the electromagnetic field theory, the functional relationship between the amplitude ratio of the electromotive force amplitude signals of the two receiving coils and the water content of the seed is established. Secondly, fifty sets of theoretical values of the mentioned model can be obtained through simulation analysis. Finally, comparative tests are carried out by using soybean seeds. The experimental results preliminarily verify the feasibility of the electromagnetic measurement method of the water content of the seed. The advantage of the proposed method is that the measurement of the water content of the seed is non-contacting.

The resonant frequency of an antenna plays a crucial role in the design of a reconfigurable antenna. In this article, we have developed a dual-band reconfigurable terahertz patch antenna by using graphene. The simulation results demonstrate that the designed structure can provide excellent properties in terms of dual wide-band performance, frequency-reconguration by applying different voltages on the graphene. These initial results are particularly promising for various applications in the THz regime. Furthermore, we have investigated the effect of the additional parameter such as temperature and relaxation time. The modeling is done by using a new equation of the Wave Concept Iterative Process (WCIP) method, and the validation is achieved by comparison with CST simulator. Here, we propose to develop a new efficient and flexible numerical tool for graphene modeling.

A coplanar waveguide (CPW) fed folded dipole with a 20% impedance bandwidth and 4-6 dBi endfire gain with stable patterns is proposed. Since the proposed element is electrically large (2.1λ x 2λ) conformal topology of this endfire radiator is designed and characterized. The input impedance is not altered significantly compared to the planar element. The radiation in the H plane indicates an increase in specific absorption rate when integrated with a typical mobile terminal. In order to mitigate this effect, a compact (0.8λ x 0.8λ) wideband reflector with periodic sinusoidal slots is proposed and mounted with the conformal element at an offset of 0.2λ from the radiator. The proposed antenna has an operating bandwidth from 24 to 30 GHz (20%) with an endfire gain of 6-7 dBi across the band. The front to back ratio is more than 12 dB across the band. Pattern diversity of the conformal antenna is also investigated. Simulated and measurement results are presented in detail.

Printed, circularly polarised, microstrip line fed antenna having asymmetric slotted structure is presented. Two antennas, antenna 1 (A1) and antenna 2 (A2), having the same design but radiating with opposite senses of circular polarisation are fabricated. The geometrical structure consists of uneven combination of elements fixed through parametric variations. The measurements yielded significant impedance bandwidth (IBW) and axial ratio bandwidth (ARBW) for axial ratio (AR) ≤ 3 dB. A1 offered IBW of 9.67 GHz (2.46-12.13 GHz, 132.6%), ARBW of 7 GHz (4-11 GHz, 93.33%) and a peak realised gain of 4.05 dBi. A2 offered IBW of 10.05 GHz (2.55-12.6 GHz, 132.7%), ARBW of 7.3 GHz (3.9-11.2 GHz, 96.7%) and a peak realised gain of 4.1 dBi. This constitutes a wide coverage of over 88% of the ultra-wideband (UWB) spectrum (3.1-10.6 GHz). Omnidirectional radiation patterns and marginal group delays are the other features of these antennas. The proposed design is validated through simulations and experimental investigations.

A medium-gain vertically polarized omnidirectional antenna array (VPOA) with wide bandwidth is proposed in this paper. Initially, a conventional printed dipole antenna with integrated balun (IB) is introduced to use as the wideband element. Then, four antenna elements are alternately arranged in the vertical direction to achieve high gain. Moreover, the four elements are excited by a shunt-fed feeding network which is utilized to provide uniform amplitude and phase for the elements. The feeding network has a common ground with the balun, and it can be easily integrated with the IB. Furthermore, two metallic cylinders placed in the normal direction of the substrate are used as two reflectors to improve the gain variation in the horizontal plane. In order to validate the design method, a prototype is fabricated and measured. The measured results indicate that the proposed antenna has an impedance bandwidth of 56% (1.12-2 GHz) for VSWR≤2 and a simple structure with lateral size of 0.45 λ₀ (λ₀ is the free-space wavelength at center frequency). In addition, stable omnidirectional radiation patterns are obtained with gains around 6.5 dB and the gain variations in the horizontal plane less than 2 dB across the operating band.

This paper introduces an Ultra-Wideband (UWB) circle antenna array with beam forming techniques that combine Self-Adaptive Dynamic Differential Evolution (SADDE) which is capable to minimize the Bit Error Rate (BER) for Multi-User Multiple Input Multiple Output (MU-MIMO) in indoor communication system. By using the ray tracing techniques to compute any given indoor wireless environment, the impulse response of the system can be calculated, and the BER can be computed accordingly. Next, we analyze the BER performance of the UWB MU-MIMO system that applies beam forming for spatial division multiple accesses. Numerical results show that the SADDE can control the antenna feed length to reduce the BER and form the radiation beam pattern towards the direction of the desired signals while forming nulls to co-channel interferers for MU-MIMO system.

In this study, the physical optics approximation (POA) algorithm is described for predicting the electromagnetic (EM) scattering of three dimensional (3D) two-layer rough surfaces. The POA is initially used to calculate the composite scattering of an object and single layer rough surface for two dimensional (2D) situations. We extend this method to the case of a rough layer with two rough interfaces. The multiple coupling interactions between the upper and lower layer are considered based on an iterative strategy. Because the coupling effect is considered, the 3D model is quite time-consuming. In order to obtain numerical results rapidly, a parallel technique based on the OpenMP is adopted to accelerate the coupling iterative calculation. The model is applicable for moderate to large surface roughness. However, the rough surface should have small to moderate slopes so as to meet the conditions of POA. In numerical results, the normalized radar cross section of two-layer rough surfaces model under different polarizations is calculated, and the model is validated by comparison with a numerical reference method based on the method of moment. In addition, the influence of roughness on the scattering model is analyzed and discussed.

This letter presents a novel quad-band bandstop filter. It is formed by loading a microstrip line with two special resonators. The special resonator can be seen as a coupled-line and shorted stub-loaded half-wavelength microstrip resonator (CSSHMR). The resonator can resonate at four frequencies, which forms the corresponding equivalent shorted points at the microstrip line. Therefore, signals are rejected at these equivalent short-circuited points, which realizes the quad-band bandstop responses. The four resonant frequencies can be separately adjusted in a limited range. The gap coupling between the resonators can be introduced to adjust the performance. A transmission line model is built to analyze the quad-band bandstop filter. A prototype quad-band bandstop filter is designed, fabricated and measured. The measured and simulated results have a good agreement.

The haze-prone areas are usually places with limited transmission line corridors and large power loads. The performance of transmission lines is under threat of haze. The haze particulates around the transmission lines would be charged and affect the electric field near high voltage direct current (HVDC) transmission lines. Accoring to the influence mechanism of haze on ionized field, the electric perfromance of HVDC transmission lines under haze weather is dicussed. In the paper, an improved meshless local Petrov-Galerkin method (MLPG) is proposed to investigate the distribution of ionized electric field, and example of an actual transmission line is studied to verify the validation of the proposed method at first. It is proved that the proposed method agrees well with the measurements. Then the ionized field distribution under different haze weather levels is discussed, as well as the influenced factor. Results indicate that the ionized electric field and ion current density on the ground would increase under haze weather, but with the similar trends to good weather condition. Meanwhile, the haze weather levels have greater influence on the ionized electric field than ion current density, where the increase of corona and space charge are the main reasons.

For wireless power transfer via magnetic resonant coupling (MRC-WPT), magnetic coupling between resonant coils can be greatly enhanced when a ferrite core is introduced inside the coils. Based on the equivalent circuit model of wireless power transfer system, transfer characteristics of the MRC-WPT system with air resonant coils and a ferrite core are respectively analyzed in this paper. The influence mechanism of the load on the power transfer efficiency is investigated. Also, the requirement of load for improving transfer efficiency is derived when adding the ferrite core to the system. The numerical simulation and experiment result indicate that the transmission efficiency in the MRC-WPT system with ferrite core is higher than that in the counterpart with air resonant coils in the whole transfer region when the load is larger than the maximal critical load. In addition, for different transfer distances, the system efficiency for the system using the ferrite core tends to become lower than that in the air coil system when the load is smaller than the critical load.

By taking into account the facts that thick dielectrics are required for low frequency absorbers, that thick dielectrics are not always flexible, and that targets are not always planar, an efficient tool for the systematic design of flexible broadband radar absorbers using the least-square method is presented in this paper. Two approaches for designing the physical model of the absorber are presented. The first one consists of resistive square loops deposited on top of a dielectric, and the second one consists of metallic square loops associated with lumped resistors. More than 90% of absorption rate is obtained in the required bandwidth for both transverse electric and transverse magnetic polarizations with the two approaches and achieving a performance of operational bandwidth to thickness ratio of 7.69. Finally, the required dimensions of flexible absorbers in some low frequency bands are given in order to show the versatility of the approach.

Recently, the introduction of surface phase in Snell's law and Huygens' phenomena leads to ultrathin phased surfaces which can tailor the transmission and scattering of the incident wavefront in many ways. In this article, a remodeled Jerusalem cross used as the meta-element whose geometrical parameters are varied to obtain 360° phase variation, and a 3-bit quantization is presented to design phase coded surfaces to manipulate (focusing and splitting) normally incident beam. Further, two 3-bit phase quantized supercells of approximately 2λ length and width are proposed and simulated (3x3 matrix arrangement) to test and compare the scattering properties with traditional chessboard type supercell. Obtained simulated results show diffused reflections for both the models and reduced intensity of four corner lobes in comparison to chessboard supercells (at θ=30˚ and ϕ=45˚). Experimentally recorded monostatic RCS of model-2 prototype has a close agreement with the simulated results and more than 10 dBsm RCS reduction observed from 9 GHz-11 GHz.

In this letter a novel microfluidic reconfigurable filter is presented at 1, 1.4 and 1.8 GHz. This triple band filter is based on dual-mode ring resonators where metal-liquid switches are used for interconnection of different resonators and feed lines, therefore, allowing tuning of its center frequency as well as of its external Q. Simulated and experimental results are shown with good agreement.