A technique for converting a wide-band coplanar waveguide fed antenna to UWB by positioning slots in the modified ground plane (MGP) adjacent to the feed is proposed in this paper. The slots can be symmetrically or asymmetrically positioned for optimum performance. One slot pair is initially positioned through parametric analysis in the modified ground plane at an equal distance from the feed end for the maximum achievable impedance bandwidth. The second slot pair is similarly positioned, optimising the antenna for ultra wideband operation. Two CPW fed antenna geometries are experimented using the technique, one unique and the other, a generic circular monopole. Both antennas have MGP and are fabricated on an FR4 substrate. The analysis and simulation have been done in FEM based High Frequency Structure Simulator (HFSS). The performance of the two antennas is measured with a Vector Network Analyzer ‘Agilent PNAE8362B'. The impedance bandwidth and radiation pattern validate the performance of the antennas for ultra wideband applications. The experimentally obtained bandwidth precisely covers UWB, and principal patterns are uniform throughout the band.

One of the faults in medium voltage (MV) overhead power line is a high impedance fault (HIF) owing to low-current discharge to a tree (THIF). This type of fault generates signals in wide frequency bandwidth which may lead to electromagnetic interference (EMI) with neighboring devices and consequently results in degradation in the performance of nearby systems. This problem becomes more critical when MV power lines path is located in a wooded area in which there will be frequent transient conflicts between trees and power lines especially in the windy conditions. Given the importance of this issue, the ability of THIF to generate EMI is first demonstrated in this paper. Thereafter, a hybrid technique based on combination of quantile regression (QR) and empirical mode decomposition (EMD) is proposed to perform a feature extraction from THIF signals. By comparing the QR results of different samples of THIF signal with other similar signals, the validation of proposed method is depicted. In summary, the original contributions of current research include 1) assessing EMI due to THIFs, 2) using EMD in pre-processing of THIFs signals and extracting their main components, 3) recommending QR for the feature definition of THIF.

Nonlinear characteristics of semiconductor devices play a key role in the performances of circuits, but their modelling is still a big challenge in circuit simulations nowadays. This paper explores modelling nonlinear characteristics of circuits containing semiconductor devices by presenting a modified physically based simulation method. A p-i-n diode microstrip circuit is taken as a sample, and its nonlinear characteristics, such as the power limiting, bistability, and forward recovery characteristics, are simulated and analysed. The applied method demonstrates its good capability and accuracy of modelling the nonlinear characteristics in the simulation, and moreover clarifies the underlying physical mechanisms. In contrast, the Advanced Design System (ADS) software, a popular circuit simulation program based on the equivalent circuit model, fails to reveal some of those nonlinear characteristics.

The currents flowing through a transmission line produce a rotating magnetic field of vertical and horizontal components which are orthogonal in space and vary with time. Buried and aerial metallic pipelines that run parallel to or are placed in the vicinity of overhead AC high voltage transmission lines are affected by this field resulting in an induced voltage on the pipelines. Several related studies and safety standards dealing with this problem have been published. Nevertheless on a multi-circuit line, the issue of current phase shift variation has not been fully covered yet. This paper provides a detailed analysis of the effect of current phase shifts on the magnetic field distribution and polarization pattern around power lines using analytical approach from electromagnetic field theory. In this study, not only the variation of the filed distribution with phase arrangements and phase shifts is further established, but also the characteristic nature of the variation of the field distributions for six phase arrangements is examined in more detail. The results show that the magnetic field distribution at the ground level and the spatial distribution of the magnetic field polarization ratio vary significantly with the phase sequence arrangement as well as the current phase shifts between the two circuits. The field polarization differs at different locations. The information from the results can be useful for consideration in designing an effective AC mitigation technique and in placing pipelines in the utility corridor with power lines. Pipelines should be placed in a region of minimum field intensity within the right-of-way of the line, in order to have minimal induction on the pipeline in normal operating conditions of the line.

Point target detection in space-based infrared (IR) imaging system is an important task in many applications such as IR searching and tracking and remote sensing. Although it has attracted great interest and tremendous efforts during last decades, it remains a challenging problem due to the uncertain heterogeneous background and the limited processing resources on the onboard platform. Aiming at this problem, a novel background suppression method based on multi-direction filtering fusion is proposed in this paper. The process of background prediction for each pixel by this method can be divided into two steps. Firstly, eight predicted values are obtained by using linear filtering methods along eight different directions respectively. Then, Gaussian weighted sum of the eight predicted values is computed to generate the final result. We conduct several groups of experiments on different categories scenes with simulated targets, and the final experimental results demonstrate that our methods can not only obtain state-of-the-art performance on background suppression (especially for heterogeneous backgrounds), but also detect targets accurately with low false alarm rate and high speed in IR point target detection tasks.

In this paper, a CPW-fed circular patch UWB-extended bandwidth antenna is proposed which is fabricated and characterized on silicon. The proposed antenna covers fractional bandwidth of 132.08% with high rejection triple band-notch characteristics [WiMAX(3.30 GHz-3.80 GHz)/WLAN(IEEE802.11a/h/j/n 5.15 GHz-5.35 GHz, 5.25 GHz-5.35 GHz, 5.47 GHz-5.725 GHz, 5.725 GHz-5.825 GHz)/X-band downlink satellite communication system (7.25 GHz-7.75 GHz)]. Gain and efficiency of the proposed antenna in the entire bandwidth vary between 3.96 dBi-10.98 dBi and 84%-95%, respectively. Also, group delay in the entire operating band is ≤ 1.0 ns. Furthermore, the proposed antenna exhibits good dipole like radiation pattern in E-plane and omnidirectional pattern in H-plane with small dimension of 20×20×0.5 mm³.

Aimed at solving the problems of high initial cutoff frequency, small stopband range and poor inhibition in the current electromagnetic band gap (EBG) structure, an electromagnetic band gap structure designed on the basis of periodic Z-bridge EBG inserted by a double complementary slit ring resonator (DBCSRR) cell is proposed. Compared with the traditional EBG structure, the proposed EBG structure can achieve 270 MHz-20 GHz bandwidth in a reference of -30 dB, which is wide in range. The measured and simulated results indicate the wideband of noise suppression. In addition, the lower and upper cutoff frequencies are estimated by using equivalent circuit models, respectively. Moreover, the IR-Drop and dc resistance is accurately investigated through 3-D simulations. Finally, the transfer characteristics of single signal line are studied.

Based on metamaterials and compressive sensing theory, we design a single pixel millimeter-wave fast imaging system by a 1D aperture array. The aperture array is realized by a column of complementary electric-lc (cELC) units etched on amicrostrip transmission line. Each cELC unit resonates at a different frequency, where the energy is coupled from the aperture to free space. A sequence of random field patterns can be obtained by controlling geometric parameters of each cELCunit. We use the frequency as the index of measurement matrix which well satisfies the restricted isometry property (RIP) and is well suited for compressive sensing (CS). A prototype of CS imaging system operatingatKa-band (27-40 GHz) is fabricated which can detect a 5 cm * 5 cm object precisely at a distance of 50 cm.

An extremely wideband photonic crystal antenna is proposed with a very compact size of 16.6 x 26.6 x 0.9mm³. The double-layer materials of silicon and glass are selected as the antenna substrate. The band gap performance of photonic crystals can decrease electromagnetic wave absorption of silicon substrate, restrain surface wave loss of antenna, and increase electromagnetic wave space radiation. Hence the periodical photonic crystal with square lattices is applied in upper silicon substrate. The glass substrate not only decreases effective dielectric constant of antenna, but also supports silicon substrate with photonic crystal. MEMS processes are used to realize photonic crystal antenna with plenty tiny through-holes. The simulated and measured results demonstrate that photonic crystal can effectively expand the working bandwidth of base antenna.

This paper analyzes rectangular and circular patch antennas fabricated from meshed conductors and backed with solid ground planes. Because of the meshing, the antennas are rendered optically transparent, where the transparency is determined by the mesh geometry. It is found that although there is a compromise between the antenna's efficiency and the optical transparency of the meshed patch, it is possible to optimize the antenna by refining mesh lines to certain extent. The limiting factors for refining mesh lines include material handling and fabrication process as well as the increased line impedance when being refined, which accordingly causes loss in antenna's efficiency. A refined mesh with thin linewidth increases both antenna performance and transparency. Additionally, it is found that the reduction of certain mesh lines increases the optical transparency with minimal hindrance to the antenna's efficiency, leading to further enhancement to the see-through percentage. Although it is possible to refine mesh lines to improve the antenna's efficiency or gain, it is seen that there is a limit for such an optimization method. This limit is closer to the efficiency of a solid patch for a lower transparency, whereas it is lower for increased transparency. Cross polarization level was also examined, and there was no signifficant efft on such a parameter due to meshing.

This paper aims at designing a wideband planar inverted F antenna (PIFA). The design of a PIFA begins with an elementary step such as the etching of antenna element pattern in a metal trace. After the etching adherence is developed by incorporating bonding between it and a printed circuit board which is primarily an insulating dielectric substrate. A ground plane is developed by a prolonging metallic layer which is adhered to the opposite side of the substrate. The simulation is done using ANSYS HFSS full wave 3D simulation software. The proposed PIFA is very compact and also provides a gain of 2.86 dB. As a consequence of the exemplary feature like an omnidirectional radiation pattern, there is an exceptional improvement in coverage. Moreover, the frequency bands covered by the PIFA are for applications including USPCS, UMTS, ISM/Bluetooth and WLAN at (1.85 to 1.99) GHz, (1.90 to 2.20) GHz, (2.4 to 2.485) GHz and (5.1 to 5.90) GHz, respectively.

In this correspondence, the two-dimensional (2-D) direction-of-arrival (DOA) estimation problem for partially polarized (PP) signals is considered. In particular, we focus on an array geometry containing three identical uniform linear arrays (ULAs). Compared with existing methods, the proposed one has three main advantages. Firstly, the estimation accuracy is higher since it exploits the polarization information. Secondly, it can work effectively under the coexistence of both noncircular and circular signals. Finally, pair matching for 2-D DOA is not required which reduces the computational complexity. Simulation results are presented verifying the efficacy of the algorithm.

A compact directional MIMO antenna operating in 2.4 and 5 GHz wireless local area network (WLAN) bands is presented. The compactness of the proposed multiple-input multiple-output (MIMO) antenna can be attained through using miniaturized antenna elements and meanwhile employing an extremely narrow edge-to-edge inter-element space (3 mm). Two novel miniaturized planar inverted-F antenna (PIFA) elements which share a common ground are designed, and each element has a dimension of 31 mm × 17 mm and a profile of 4.2 mm. By etching three slots on the ground, the port isolation can be significantly enhanced, which can even reach a maximum of 54 dB at 2.45 GHz. A desirable directional radiation pattern is obtained, and the calculated envelope correlation coefficient is better than 0.01.

The development of near-space hypersonic vehicles is confronted with the ``blackout'' problem of the plasma sheath. As electronic density on the leeward surface is lower than that on the windward surface during the reentry process, a low Earth orbit (LEO) satellite may be used to mitigate this problem. In this study, the Iridium system, as a low-orbit relay satellite system, is utilized to evaluate the feasibility of using a LEO satellite. First, the incident angle of the electromagnetic waves radiating from the vehicles to various potential relay satellites is calculated by the STK software. Second, the transmission coefficient of the electromagnetic wave in the plasma is obtained by using the equivalent wave impedance method to present the attenuation effect of the plasma sheath channel. Finally, the attenuation coefficients of each channel between the aircraft and the potential satellite are used as a parameter to select the best relay in the reentry process of the vehicles. Simulation results show that the use of LEO satellites for relay can significantly reduce the communication interruption time during the reentry process by 32.6% for typical scenarios.

This paper describes the design and experimental characterization of a circular polarized printed antenna for dual-band WiFi operation at 2.45 GHz and 5.10 GHz. The patch design is based on a combination of slits loading and gap-coupling applied to a disc patch in order to enhance the radiation performances in terms of polarization purity and bandwidth at the two operation frequencies. Experimental validations confirm a maximum gain around 6.0 dB for both 2.45 and 5.10 GHz, as well as an axial ratio as low as 0.5 dB and a return loss exceeding 15 dB on the operating frequencies. These characteristics are suitable for operationing in IEEE802.11x networks.

Wearable wireless technology has developed as an exciting topic over the last couple of years. With the extensive use of Wearable Wireless Devices (WWD) in greater proximity to the body for various wireless applications, the concern about biological effects due to the interaction of human tissues with the radiations is growing. In this research, we investigate the application of Infrared Thermography (IRT) to obtain temperature dynamics and reconstruct Specific Absorption Rate (SAR) to evaluate the exposure amenability of WWDs. A microstrip monopole antenna on a wearable substrate is used to determine the biological effects of the interaction of electromagnetic (EM) waves on the body. SAR is obtained using EM field simulations and by reconstruction from thermal measurements with the use of Bio-heat equationsfor a continuous exposure of 300 s. Validation of IRT to reconstruct SAR is demonstrated by comparison with EM computations. The maximum SAR was 32 mW/kg, for simulations and 35 mW/kg, from reconstruction after IRT experiments. The maximum temperature change in both cases was always less than 1˚C. The difference between the SAR obtained through IRT and simulation tools accounted for an average of 8.7%. Information acquired using IR temperature dynamics can yield SAR values which can assess radio frequency exposure compliance for WWD at frequencies used for modern wireless technologies, with reliability.

A semi-analytical method to analyze post-wall waveguides and circuits based on the model of two-dimensional photonic crystals formed by layered periodic arrays of circular cylinders is presented. The propagation constant of the fundamental TE mode, the attenuation constant due to the leakage loss and the effective width of an equivalent rectangular waveguide are calculated. Using the concept of the effective width, the original structure is replaced by an equivalent rectangular structure. When additional metallic posts are loaded in the rectangular waveguide, functional post-wall waveguide-based passive circuits are formed. The S-parameters of the post-wall circuits, which act as bandpass filters, are calculated using the image theory combined with the lattice sums technique.

This paper presents the development and design of flexible and conformal printed monopoles antennas. The main objective is to control the level of radiation in broadside antenna from zero to a maximum by changing the curvature of printed board. Two printed antennas types are considered: thin wire and disk monopole. Furthermore, with the curving radius R increasing, the classical null on the broadside radiation pattern disappears gradually for both wire and disk. Increasing the curvature radius of conformal flexible antenna, and keeping all other parameter's value, wire monopole antenna becomes mismatched while the disk monopole antenna remains matched for all radius of curvature. The simulated results of various monopoles are compared successfully with measurements.

A dual-band omnidirectional circularly polarized (CP) patch antenna with conical radiation patterns is presented in this paper. The antenna consists of a patch with inclined slots, a ground plane with L-shaped slots and a coaxial probe. In addition, by loading shorting vias between the patch and the ground plane, the vertical polarizations of the proposed antenna at TM₀₁ and TM₀₂ modes can be obtained. Two sets of slots etched on the ground and the patch contribute to the horizontal polarizations for the two modes, respectively. Omnidirectional CP fields can be achieved at both resonant modes when the two orthogonal polarizations are equal in amplitude and different in phase by 90°. To verify the design, a prototype operating at 2.4 GHz WLAN and 3.5 GHz WiMAX bands has been fabricated and measured. The measured average axial ratios (ARs) at two resonant modes in the azimuth plane are 1.1 and 1.5 dB, respectively. Experimental results show good agreement with the simulated data.

This paper extends the parabolic integral equation method, which is very effective for forward scattering from one-dimensional rough surfaces, to include backscatter. This is done by applying left-right splitting to a modied two-way governing integral operator, to express the solution as a series of Volterra operators; this series describes successively higher-order surface interactions between forward and backward going components, and allows highly efficient numerical evaluation. This and equivalent methods such as ordered multiple interactions have been developed for the full Helmholtz integral equations, but not previously applied to the parabolic Green's function. Equations are derived for both Dirichlet and Neumann boundary conditions (TE and TM).