A tri-band slotted F-shaped antenna with dual-polarization characteristics for wireless applications is presented. The crooked gap and F-shaped monopole are optimized to achieve tri-band operation of 2.4, 3.5 and 5.8 GHz with -10 dB impedance bandwidths of 20%, 14.1%, and 13.6%, respectively. Furthermore, by properly inserting an F-shaped strip on the wide-slot ground, the circular polarization (CP) with a 19% (3.3-4 GHz) 3dB axial ratio bandwidth is obtained. The proposed antenna has a compact dimension of 42×40×1.6 mm³. A prototype of the antenna is fabricated and tested, and an agreement with simulated results is obtained.

An efficient approach is presented for the design of a low sidelobe four-dimensional (4D) planar antenna array, taking into account mutual coupling and platform effect. The approach is based on the combination of the active element patterns and the differential evolution (DE) algorithm. Different from linear and circular arrays, the mutual coupling compensation in a planar array is more complicated since it requires numerous data of the active element patterns in different azimuth planes. In order to solve this problem, a useful interface program is developed to get these data from commercial software HFSS automatically. Also different from conventional low sidelobe arrays with tapered amplitude excitations, the low sidelobe in the 4D array is realized using time-modulation technique under uniform static amplitude and phase conditions. The DE algorithm is used to optimize the time sequences which are equivalent to the complex excitations in conventional arrays. Both computed results and simulated results in HFSS show that a -30 dB sidelobe pattern can be synthesized in a 76-element planar array with an octagonal ground plane and a radome, thus verifying the proposed approach.

This work presents a self-consistent and self-contained model to study and analyze aircraft-lightning electrodynamics. In this paper we review the well developed and reported transmission line model of the cloud-to-ground (CG) lightning return stroke. Subsequently, the incorporation of a circuit model of the aircraft into the return stroke model is considered. The direct hit characteristics of aircraft body lightning currents for both CG and GC (ground-to-cloud) are important when designing protection, shielding and filtering systems for airborne electronic and electrical systems within the aircraft system. Moreover, the model will allow design of aircraft structure and geometry to minimize energy dissipation into the aircraft structure and systems. Basic electromagnetic theory is used to show the validity of considering the return stroke as a transverse magnetic wave along a transmission line. A distributed transmission line model for the aircraft and the return stroke channel of the lightning is used to simulate the return strokes of CG and GC flashes. The effects of the aircraft geometry with sharp edges are included in the computation of aircraft capacitance values, both distributed as well as lumped values. The paper compares electric currents, channel voltages, the rate of change of current and the frequency spectrum along the lightning channel of the return strokes for CG and GC flashes with aircraft attached to the channel.

A hybrid method, combining analytic Kirchhoff approximation (KA) and numerical method of moments (MoMs), is developed to solve the two-dimensional (2D) scattering problem of a dielectric target with arbitrary cross section above a moderate perfect electric conductor (PEC) rough surface under TE-polarized tapered wave incidence. The induced current on the rough surface is analytically expressed using the KA method, which depends on the tapered incident wave and the field illuminating by current distribution on the target, leaving only unknown induced current on the target. So the electric field integral equations of the induced currents on the target only can be derived; it allows a substantial reduction of computation time and memory requirement. Furthermore, for different secondary scattering of the underlying rough surface, different truncations of the rough surface are taken to speed up computation of the scattering contribution from the rough surface to the target. Making use of Monte Carlo realization, bistatic scattering from a cylindrical target above a PEC rough surface is well simulated to test validity and efficiency of the proposed method. Numerical results from the hybrid method have good agreements with those from the conventional method of moments. However, the computational time and the memory requirements have been greatly reduced.

A novel kind of symmetrical backward-wave coupled-line coupler with arbitrary coupling level is proposed in this paper which is based on resonant-type composite right-/left-handed transmission lines (CRLH TLs). First, an equivalent circuit model and procedure for circuit parameters extraction are presented to reveal the inherent nature of the unit cell of the CRLH coupler. Then a CRLH TL composed of four cascaded unit cells is demonstrated to point out the way to achieve balanced condition. At last, even/odd modes analysis based on full-wave simulation is employed to explain the operating principle of the coupler. Both quasi 0-dB and 3-dB CRLH couplers are demonstrated experimentally. The quasi 0-dB backward coupling is achieved over the range from 1.69 GHz to 2.19 GHz (-3 dB bandwidth in measurement), which represents the fractional bandwidth 25.8%. The maximum coupling coefficient 0.52 dB is obtained at 1.96 GHz, where the directivity and isolation is 20.8 dB and 21.3 dB, respectively. The 3-dB couplers shows an amplitude balance of 2 dB and quadrature phase balance of 90±5 degree over the fractional bandwidth of around 11.4%, from 1.99 to 2.23 GHz.

This paper proposes a leaky wave slot antenna array for azimuthally omnidirectional coverage. Slot elements were arranged in cascade and series-fed by a coplanar waveguide (CPW). The most important novelty of this paper is that the whole array, including all the radiating elements and feeding structures, was arranged on a single metal layer. This simple structure has the merits of easy fabrication and low cost, especially at higher frequencies, such as millimeter wave band. Moreover, the proposed antenna array was folded around a center-hollowed columnar substrate to achieve omnidirectional radiation pattern in the azimuthal plane, with the gain variation less than 1.1 dB, which is similar to previous omnidirectional antenna array. In this paper, a prototype of the proposed antenna array at 2.3 GHz was built and tested to validate the design strategy. The measured results, including S parameters, radiation patterns, and gain, were found to agree well with the simulation ones.

In most existing transmitted-reference ultra-wideband (TR-UWB) communication systems, receivers use the standard Gaussian approximation (SGA) for multiuser interference (MUI). It is an assumption used in most conventional multiuser systems, where the MUI tends to a Gaussian process by the central limit theorem, and convergence is relatively fast with respect to the number of users. However, for TR-UWB systems which are developed for short-range applications, we have a small number of active users. In this case, significant performance degradation is found in TR-UWB receivers due to the impreciseness of SGA. In this paper, we show that the Middleton class-A model is a more appropriate statistical model for MUI modeling in TR-UWB systems than the often used SGA. A closed-form expression for the probability density function (PDF) of the TR-UWB system under MUI, Gaussian noise and impulsive alpha-stable interference is developed. All these analytical results are confirmed by numerical simulations.

A novel design of circularly polarized (CP) annular-ring microstrip antenna (ARMSA) working in TM11 mode is presented. The CP radiations of the proposed antenna are implemented by a 90° branch-line hybrid coupler placed at the inner part of the ARMSA. Since the ARMSA has narrow bandwidth and high-input impedance, a circular parasitic patch suspended above the ring is employed for not only improving the impedance matching and bandwidth, but enhancing the performances of axial ratio (AR). Due to the utilizing of parasitic patch and circular hybrid, the measured results are shown to attain a 10-dB return loss bandwidth of 31.2% (1300-1780 MHz) and a 3-dB AR bandwidth of 19.2% (1360-1650 MHz) respectively. The CP gain is 8.2 dB at 1.575 GHz. The proposed antenna is low profile and has a simple structure, therefore, it can be a good candidate for GPS portable terminal applications.

A novel wideband bandpass filter on a triple-mode slotline ring resonator is proposed in this letter. By attaching two stubs with different lengths and/or widths to the symmetric plane of a slotline ring resonator, the frequencies of first three resonant modes can be rearranged towards quasi-equal separation. By feeding this slotline resonator using the microstrip feed lines at positions with an angle of 90° to the symmetrical plane, these three resonant modes can be simultaneously raised up, aiming to form up a wide passband. Meanwhile, a wide upper-stopband can be realized by setting the lengths of two stubs unequally. After the principle of an initial wideband filter is described, a prototype of compact filter with internally-loaded stubs is designed with fractional bandwidth of 66% at center frequency of 3.0 GHz. Measured results well validate the predicted ones.

Recently, a new radiation model for the partial element equivalent circuit (PEEC) technique has been proposed. This model makes use of the concept of generalized complex inductance to account for the radiation effect and preserve the (quasi-)static condition for the capacitance. Therefore, PEEC models with the radiation effect included consists of real-valued capacitors but complex-valued inductors. In this paper, a method for deriving a concise and physically intuitive equivalent circuit from such a radiating PEEC model is presented. The method is based on the Y-to-Δ transformation to eliminate all "unimportant" internal circuit nodes and results in an equivalent circuit with only a few nodes left. The equivalent circuit for a short electric dipole is first derived analytically to offer a simple explanation to the basic principles. The proposed method is then applied to several practical and electrically small antennas for more detailed demonstrations. Numerical results obtained from these examples suggest that a physically intuitive circuit model can potentially be derived for arbitrary radiating multi-conductor structures, showing the method is useful for analysis and design of modern integrated and electrically small antennas.

In this paper, new miniaturized hybrid branch line couplers loaded by square-split ring resonators are proposed. This loading technique increases the electrical length of transmission lines by patterning the ground plane under the conductor trace in microstrip lines with the complementary, dual-behavior, configuration of square-split ring resonators. Each branch is loaded by one resonator in the first coupler and by two resonators in the second coupler. Hence, compact sizes of 9.29 mm × 9.57 mm, and 8.88 mm × 9.11 mm, or equivalently 0.2λg × 0.2λg and 0.19λg × 0.19λg, respectively, are obtained at the operation frequency, 2.4 GHz. This corresponds to 66.14% and 60.18% of a conventional structure's area, respectively. Moreover, the new designs can suppress higher harmonic components due to the bandstop response of the square-split resonators at their resonant frequency while maintaining similar measured performance compared to the conventional branch-line hybrid coupler. Measured and simulated responses are in very good agreement which validates the proposed structures and technique. This technique can also be applied to minimize the size of other microwave circuits.

A novel bandstop filter with wide-stopband performance is proposed and discussed in this paper. This circuit configuration includes two-section coupled lines and three open-circuit transmission-line stubs. Due to the symmetry of this proposed structure, closed-form equations for scattering parameters are investigated. Transmission zeros and poles location for different circuit parameters are discussed, and the corresponding design curves are given. In order to verify this new filter circuit structure and its corresponding design theory, several typical numerical examples are designed, calculated and illustrated. Furthermore, a practical wideband bandstop filter with -20 dB fractional bandwidth of 94% centered at 3 GHz with sharp rejection characteristics is fabricated to validate the theoretical prediction. The measured frequency response of the filter agrees excellently with the predicted result.

A novel compact microstrip slot antenna applied to WLAN/WiMAX applications is presented.The proposed antenna consists of a trapezoid and ellipse slot, a pair of symmetrical inverted L-strips, an elliptical-arc-shaped stub and a monopole radiator.By adjusting the dimensions and positions of these structures, the antenna can effectively generate three different resonances to cover the WLAN/WiMAX bands while maintaining small size and simple structure.Based on this concept,a prototype of the proposed antenna has been successfully fabricated and measured.The experimental and numerical results show that the antenna has impedance bandwidth with 10 dB return lossof 360 MHz (2.33-2.69 GHz) and 2630 MHz (3.24-5.87 GHz), which can cover both the WLAN 2.4/5.2/5.8 GHz bands and the WiMAX 2.5/3.5/5.5 GHz bands. In addition, good monopole-like radiation characteristics with sufficient antenna gains are obtained over the operating bands.

In this paper, a dual-band chiral metamaterial (CMM) based on cross-wire structure is proposed and studied numerically. It exhibits dual-band giant optical activity and negative refractive index in terahertz region. The surface current distributions are calculated to explain original physics. The further numerical results show that the effective frequency bands of the CMMs can be independent adjusted easily by changing the structure geometrical parameter. The designed dual-band terahertz CMMs offer flexibility in the investigation of novel terahertz device application.

A network analyzer with a bulk current injection (BCI) probe is proposed to measure the common-mode conversion coefficient for DC supply loops on a driver PCB of thin film transistor-liquid crystal display (TFT-LCD) panel. The proposed technique is used to predict the common-mode radiated emission caused by the DC supply loops, which highly correlates with the radiated emission measurements obtained for the TFT-LCD panel in a fully anechoic chamber (FAC). The proposed technique is also successful to estimate the reduction of a specific peak in the radiated emission spectrum by shielding the DC supply loops on a driver PCB of TFT-LCD panel. Electromagnetic simulation and equivalent-circuit modeling approaches are developed to confirm the common-mode radiation mechanism in this study.

The radiation characteristics of dielectric slabs over a transmission waveguide, based on the concept of spoof surface plasmons, are studied in this paper. The proposed structure can be used to control the radiation over a wide band of operation, whilst retaining low Side Lobe Levels (SLLs) and cross-polarization. Leaky modes, broadside radiation and directive beams at fixed angles can all be obtained using various configurations (utilising homogeneous or gradient index dielectric slabs). The proposed antenna design has attractive performance for THz detectors and transmitters.

This paper discusses performance improvement with the integration of an artificial magnetic conductor (AMC) into array antennas. An AMC with defected ground structure (DGS) was designed to construct the AMC ground plane and in-phase superstrate. The two distinguishable structures were integrated into an array antenna, which serves as a reference antenna at 5.8 GHz. The impedance bandwidth (BW) of the reference antenna significantly improved to 287% when integrated with an AMC ground plane and with 37% reduced size. On the other hand, the integration of in-phase superstrate effectively enhances the gain and BW of the reference antenna by 1 dBi and 44%, respectively. The effects of air gaps on the reference antenna with both the AMC ground plane and in-phase superstrate are discussed. The antenna performance factors, such as return loss and radiation pattern, are also discussed for the reference antenna, the reference antenna with the AMC ground plane, and the reference antenna with in-phase superstrate, respectively. There is satisfactorily good agreement between the simulation and measurement results. The proposed antenna is useful in WLAN (5.15-5.35 GHz and 5.725-5.825 GHz) and WiMAX (5.725-5.825 GHz) applications.

The purpose of this paper is to propose analytical and finite element method (FEM) designs of a novel three-phase Seven Layers Switched Reluctance Motor (SLSRM) for the applications which dictated by the performance with the total torque per volume as a key marker indicator. The introduced motor consists of seven magnetically independent stator layers, which each layer includes a set of 4 by4 stator/rotor poles. In this SLSRM, the three layers are energized together to produce high torque and also decrease the torque ripple in comparison with the one layer conventional SRM. Since each layer has its independent phase in the motor, the isolation problem of coils and cooling troublesome existing in conventional SRMs is solved. In addition, these types of SLSRM have some other advantages, like simpler configuration, cooling in easier way, etc. Firstly an analytical design is carried out to illustrate the design procedure and then three-dimensional (3-D) magneto static simulation analysis of the SLSRM and the one layer SRM is performed using 3-D FEM, to obtain and verify the flux-linkage, flux density and torque profiles. Also, the proposed motor is compared with a conventional one layer SRM with a same size and volume.

In this paper, we have addressed three major problems of uniform linear array in case of a sensor failure at any position. We assume that sensor position is known. The problems include increase in sidelobe levels, displacement of nulls and diminishing of null depth. The desired null depth is achieved by making the weight of symmetrical counterpart element passive. Genetic algorithm (GA) along with pattern search (PS) is used for reduction of sidelobe levels, and adjustment of nulls. Fitness function minimizing the error between the desired and estimated beam pattern along with null constraints is used. Simulation results for diversified scenarios have been given to demonstrate the validity and performance of the proposed algorithm.

We propose a methodic approach to design Artificial Magnetic Materials (AMM) with desired magnetic properties. The design procedure is defined based on a novel formulation for characterizing AMMs. The employed formulation expresses the effective permeability and the magnetic loss tangent (MLT) in terms of the geometrical and physical parameters of the inclusions. The method comprised four steps. In the first step, the feasibility of the design is checked through a set of constraints. The second and third steps provide an iterative procedure to capture the desired magnetic properties. Finally, the geometrical elements, i.e., the area and perimeter of inclusions, are calculated. The technique is applied to design of an AMM structure based on Rose curve resonators. The design based on the proposed methodology is verified by the numerical simulation of the AMM.