A circularly polarized (CP) elliptical-ring slot antenna is proposed. A tapered slot is excited by an L-shaped coupling strip. A good impedance match is obtained, and an excellent CP characteristic is achieved. The antenna has been investigated numerically, and prototype of the presented antenna is fabricated and tested. The measured results show that the antenna has a bandwidth of 37.5% (3.9 GHz-5.7 GHz) for return loss less than -10 dB and 34.7% (3.8 GHz-5.4 GHz) for average axial ratio (AR) less than 3 dB. The proposed antenna provides good CP performance.

A new method to find the Geometrical Optics/Uniform Theory of Diffraction reflection points over Non Uniform Rational B-Splines surfaces is presented. The approach is based on the Particle Swarm Optimization (PSO) technique, and the cost function used to find the reflection points is based on Snell's law. The technique can be used as an alternative to classic minimization techniques in cases where convergence problems arise.

A new framework for target detection in synthetic aperture radar (SAR) images is proposed. We focus on the task of locating reflective small regions using scattering centers model and clustering algorithm. Unlike most of the approaches in target detection, we address an algorithm that incorporates total variation filtering and mean shift clustering instead of parameter estimation. Our approach is validated by a series of tests on real SAR images and compared with other target detection algorithms, demonstrating that it configures a novel and efficient method for target-detection purpose.

In this paper, a new dual-band bandpass (BPF) filter with multi-spurious suppression is proposed, which is composed of step-impedance resonators (SIR) and grounded-step-impedance resonators (GSIR). It is shown that the resonant frequencies of GSIR can be obtained similar to SIR. Then, by determining the dimensions of SIR to have a specified resonant frequencies ratio, the dimensions of GSIR can be calculated. It is also shown that the coupling lengths between SIR and GSIR can create several transmissions zeros and can be used to suppress the unwanted higher order resonant frequencies. A third-order filter is designed and fabricated to operate at two WLAN frequencies of 2.45 GHz and 5.8 GHz. The measured results show a rejection level of 24 dB up to more than 17 GHz (7f₁). Simulation and measurement results are in good agreement with each other.

The analytical formulas for the average intensity and power in the bucket of the relay propagation of partially coherent cosh-Gaussian (ChG) beams in non-Kolmogorov turbulence have been derived based on the extended Huygens-Fresnel principle. The influences of the beam parameters, relay system parameters and the non-Kolmogorov turbulence parameters on relay propagation are investigated by numerical examples. Numerical results reveal that the relay propagation of the beam is different from that in the case of Kolmogorov turbulence. It is shown that the relay propagation has advantages over direct propagation, and the relay propagation of partially coherent ChG beams depends greatly on the beam parameters, relay system and the generalized exponent α . The focusability of the beam at the target in non-Kolmogorov turbulence increases with larger inner scale, larger relay system radius, smaller outer scale, and smaller generalized structure constant. The results are useful for the practical applications of relay propagation, i.e., free-space communication.

This paper describes a wideband double-dipole Yagi-Uda antenna fed by a microstrip-slot coplanar stripline transition. The conventional dipole driver of a Yagi-Uda antenna is replaced by two parallel dipoles with different lengths to achieve multi-resonances, and a small, tapered ground plane is used to allow flexibility in the placement of a pair of reflectors for effective reflection of back-radiated electromagnetic waves. The measured bandwidth of the antenna was 3.48-8.16 GHz for a -10 dB reflection coefficient, with a flat gain of 7.4 ± 0.4 dBi. A two-element array of these antennas was also constructed, with a center-to-center spacing of 36 mm (0.72 λo at 6 GHz) and a common reflector between the elements. The two-element array had a measured bandwidth of 3.56-7.92 GHz, a gain of 8.40-10.43 dBi, a cross-polarization level of <-15 dB, and a mutual coupling of <-16 dB within the impedance-matching bandwidth.

This study investigates the performance of a dipole antenna above electromagnetic bandgap (EBG) substrateswith different number of patchesto realize a low specific absorption rate (SAR) antenna for a 4G wireless communications system (3.5GHz band). A cubic head model is used fortheinitialanalysis toestimate the radiation characteristics and the SAR of the antenna. Computational results have shown that the antenna above anEBG substrate could provide a maximum reduction of 81% in the SAR and a radiation efficiency improvement of 10% when compared with theantenna above a perfect electric conductor (PEC) ground plane.However, the antenna above an EBG substrate with a lower number of patches results in a higher resonance frequency and cannot provide sufficient SAR reduction.In both the cubic and realistic head models,a similar tendency was observedin the SAR reduction capability ofthe antenna above the EBG substrates whencompared with the antenna above the PEC ground plane. For therealistic head model, the SARs of the dipole above EBGsubstrateswith 20 or 24 EBG patches can be reduced by 16% when compared to the casewith 12or16EBG patches.The variability of the SAR in the operating frequency band (|S_{1110 dB) of the antennais 5-35% for different EBG substrates.}

In this work, the propagation loss due to diffraction and insertion losses for indoor scenario at 5.6 GHz band are measured using directive antenna and a Vector Network Analyzer (VNA). It is shown that the insertion loss of a metallic door with porthole window varies from several dB due to the propagation loss via the porthole glass up to 50 dB due to the diffraction by the porthole boards when the line between the transmitting antenna and receiving one is outside the porthole glass. It is shown that the insertion loss of a 12 cm brick wall is 4.8 dB for vertical polarization while it is 6.3 dB for horizontal polarization. Also it is shown the diffraction loss due single or double concrete columns depends on the distance between the transmitting and receiving antennas.

This paper presents results of signal propagation studies for wireless sensor network planning in aquaculture environment for water quality and changes in water characteristics monitoring. Some water pollutants can cause widespread damage to marine life within a very short time period and thus wireless sensor network reliability is more critical than in crop farming. This paper shows that network coverage models and assumptions over land do not readily apply in tropical aquaculture environment where high temperatures are experienced during the day. More specifically, due to high humidity caused by evaporation, network coverage at 15 cm antenna height is better than at 5 m antenna heights due to the presence of a super-refraction (ducting) layer. For a 69 m link, the difference between the signal strength measured over several days is more than 7 dBm except under anomaly conditions. In this environment, the two-ray model has been found to provide high accuracy for signal propagation over water where there are no objects in close proximity to the propagation path. However, with vegetation in close proximity, accurate signal variation predication must consider contributions from scattered and diffused components, taking into account frequency selective fading characteristics to represent the temporal and spatial signal variations.

This paper presents a wideband model, from Direct Current (DC) to W band, for a single Anode Schottky Diode based on a commercial VDI chip. Different measurements have been performed to obtain a complete large-signal equivalent circuit model suitable for the device under consideration up to 110 GHz, and for its integration in planar circuits. The modeling has been done using a combination of DC, capacitance measurements, and RF scattering measurements. The test structure for on-wafer S-parameter characterization has been developed to obtain an equivalent circuit for Coplanar to Microstrip (CPW-Microstrip) transitions, then verified with 3D Electromagnetic (EM) tools and finally used to de-embed device measurements from empirical data results in W band. 3D EM simulation of the diodes was used to initialize the parasitic parameters. Those significant extrinsic elements were combined with the intrinsic elements. The results show that the proposed method is suitable to determine parameters of the diode model with an excellent fit with measurements. Using this model, the simulated performance for a number of diode structures has given accurate predictions up to 110 GHz. Some anomalous phenomena such as parasitic resistance dependence on frequency have been found.

An antenna consisting of a full-wavelength dipole on a GaAs membrane covered by a frequency-selective surface is proposed for improved output power from photomixers used as terahertz (THz) sources. The antenna structure reduces the vertical dimension of a typical photomixer antenna using a substrate lens while still exhibiting high total efficiency and high directivity. The resulting antenna after optimization produced an input resistance of 3870 Ω and a radiation efficiency of 60%, corresponding to a total efficiency of approximately 48.3% and a maximum directivity of 20.2 dBi at the resonance frequency of 1.03 THz. The proposed antenna is expected to be a promising alternative THz photomixer design.

The existence of drains in the field of the point source both for the spherical cavity with perfectly conducting boundary, filled with a homogeneous medium, and for unbounded Maxwell's fish eye (MFE) are rigorously proved. The existence of all class of generalized Green functions for unbounded MFE medium is established. The Green function describing the perfect focusing is found in this class. The same result for the MFE lens is obtained.

A new and exact series solution for the scattering and coupling problems by dielectric-loaded multiple slits in a perfectly conducting screen is presented. The case of normal incidence and TM polarization is considered. The scattered and transmitted elds are represented in terms of an innite series of radial modes. By applying the appropriate boundary conditions, the coecients of scattered and transmitted elds are obtained and some numerical results are given.

In order to solve the defects that the end-effect of magnetic field is ignored in two dimension (2-D) analytical method or 2-D finite element method (FEM); meanwhile, mass computer resource and time for parametric design or optimization are wasted in three dimension (3-D) FEM, a concise and efficient 3-D analytical approach is put forward for the calculation of the air-gap magnetic field and torque of coaxial magnetic gears. Based on the cylindrical coordinates where a coaxial magnetic gear is in, the equivalent current model and vector magnetic potential equation of permanent magnets in high speed permanent magnetic ring are constituted. By superposed magnetic flux density of every tile permanent magnets on high speed permanent magnetic ring in cylindrical coordinates, a air-gap magnetic field 3-D analytical formula is set up without ferromagnetic pole-pieces; in the interest of modulated air-gap magnetic field 3-D analytical formula with ferromagnetic pole-pieces, three types boundary conditions using state equations of contact surfaces between ferromagnetic pole-pieces and air-gap are established by a thorough analysis of the modulate mechanism of ferromagnetic pole-pieces. Finally, magnets of the low speed permanent magnetic ring are reduced to a distribution of equivalent current, which experience the Lorentz force in modulated magnetic field of high speed permanent magnetic ring for torque calculation. The integrals in all aforementioned calculation are axial, so the end-effect is embodied in above analytical model and more precise than 2-D analytical method or 2-D FEM. As the calculation results, the formula is accurate but faster than the 3-D FEM. The analytical model is suited for programmable calculation and that will make the structural and parametric design or optimization of coaxial magnetic gears simple and timesaving.

The phase-shifting characteristic of a novel composite right/left handed transmission line (CRLH TL) for two frequency points is analyzed in this paper. Samples of (90˚, 0˚) and (180˚, 0˚) phase-shifting TLs for two frequency points (f₁, f₂) are deigned and the total length of the CRLH TLs has decreased by more than 77% compared to the conventional microstrip lines. Then a four way power divider made by three Wilkinson power dividers and interconnected with the (90˚, 0˚) and (180˚, 0˚) phase-shifting TLs is designed to feed an antenna with two different operating modes at two different frequency bands. Four radiating patches arranging symmetrically in a loop are printed in an upper substrate and connected with the four outputs of the feed network by four copper pins. When the four rectangular patches are excited by four sources with equal amplitude and phase at f₁, metamaterial antenna with conical beam and linear polarization (LP) is achieved; while four sources with equal amplitude but 90˚ phase difference for each adjacent output at f₂ leads to wideband antenna with broadside beam and circular polarization (CP). One antenna prototype with dual-band dual-mode dual-polarization property is fabricated and good agreements between simulation and measurement results are obtained. This single-feed patch antenna is valuable in wireless communications for its radiation pattern selectivity and polarization diversity.

This paper presents comparative studies on different types of basis and testing functions used in Method of Moments (MoM) in terms of analytical complexity, convergence and condition number of the co-efficient matrix when applied to electrostatic problem of evaluating capacitance and charge distribution of conducting bodies. A thin conducting cylinder of finite length has been taken as a representative case study to evaluate the capacitance and charge distribution. The basis and testing functions which have been studied for this problem are pulse-delta, pulse-pulse, triangular-delta, triangular-pulse and triangular-triangular functions respectively. Numerical data on capacitance and charge distribution has been presented for each set of basis and testing functions in terms of condition number and convergence.

The design of a multi-channel (M = 5) lattice form band pass optical delay line filter is reported. The filter synthesis is based on the division of total transfer function into unit blocks and the circuit parameters are obtained by constrained least square method. This band pass filter has better performance compared with the results obtained in the conventional design techniques. For a filter of order 35, a stop band attenuation greater than 50dB is achieved. Further, the band pass filter is introduced in a optical fiber link and simulated in Optisystem software, to verify its characteristics.

Maxwell's equations specify that electromagnetic fields are generated by accelerating charges. However, the electromagnetic fields of an accelerating charge are seldom used to derive the electromagnetic fields of radiating systems. In this paper, the equations pertinent to the electromagnetic fields generated by accelerating charges are utilized to evaluate the electromagnetic fields of a current path of length l for the case when a pulse of current propagates with constant velocity. According to these equations, radiation is generated only at the end points of the channel where charges are being accelerated or decelerated. The electromagnetic fields of a short dipole are extracted from these equations when r>>l, where r is the distance to the point of observation. The speed of propagation of the pulse enters into the electromagnetic fields only in the terms that are second order in l and they can be neglected in the dipole approximation. The results illustrate how the radiation fields emanating from the two ends of the dipole give rise to field terms varying as 1/r and 1/r², while the time-variant stationary charges at the ends of the dipole contribute to field terms varying as 1/r² and 1/r³.

This paper presents the design, analysis, and prototyping of a novel axial-flux permanent-magnet (AFPM) motor capable of auto-starting. The preliminary design is a slot-less double-sided solid-rotor line-start AFPM motor with 4 poles for high torque density and stable rotation. One spaced raised ring was added to the inner radii of the rotor disc for smooth line-start motor. The design allows the motor to operate at both starting and synchronous speeds. The basic equations for the solid ring of the rotor of the proposed axial-flux permanent-magnet motor are presented. Non-symmetry of the designed motor led to its 3D time-stepping finite element analysis (FEA) via ANSYS 13.0, which evaluated the design parameters and predicted the transient performance. The designed motor was fabricated and tested, the experimental results showing good agreement with FEA simulation results. The prototype motor showed high starting torque and good synchronization.

Recent years, a new SAR concept based on Multi-Input Multi-Output (MIMO) configuration has demonstrated the potential advantages to simultaneously improve the performance of Synthetic Aperture Radar (SAR) imaging and ground moving target detection by utilizing multiple antennas both at transmission and reception. However, the precise signal model, as well as the effect of ground moving target in image domain and the approaches for moving target indication based on MIMO SAR system are rarely investigated. Our paper has three main contributions. Firstly, we present a detailed signal model for stationary scene and moving target based on a colocated MIMO SAR system, and analyze the motion effect of the moving target. Secondly, we provide an algorithm of phase compensation to combine the multiple virtual channel data in order to enhance the image quality. Thirdly, an adaptive optimal approach is applied for clutter suppression, then the velocity of the moving target is estimated via Delay-and-Sum (DAS) beamforming approach. Finally, several numerical experiments are provided to illustrate the derivation and analysis in this paper.