Sparse regularization imaging method (SRIM) is an effective approach to implement azimuth super-resolution for forward-looking scanning radar. However, for the scene that contains adjacent strong targets in the continuous weak background, SRIM may destroy the structure of the scene when trying to separate the closely located targets. In this paper, a divide and conquer regularization imaging method (DC-RIM) is proposed to solve this problem. Firstly, the data are divided into two channels by the mean-variance segmentation method. Normally, we consider that the data of channel I contain strong scatterers and that the data of channel II contain weak background. Afterwards, SRIM is conducted on channel I to distinguish the targets. For the data of channel II, a region enhancement regularization method is particularly proposed to acquire a good structure of the scene by making use of two-order gradient information of the data. Finally, a good imaging result can be obtained by combining the results of two channels. Experiments based on both synthetic and real data are given to verify the effectiveness of the method.

In this paper, two compact planar substrate integrated waveguide (SIW) cavity-backed antennas are proposed for wireless local area network (WLAN) at 5.5 GHz and wireless body area network (WBAN) at 5.8 GHz. The miniaturization is achieved with the concept of quarter-mode-topology, and the size of the cavity is reduced up to one-fourth of the circular SIW cavity. A L-shaped slot is etched on the top plane for miniaturization, and antenna-1 is realized which resonates at 5.5 GHz. A metal strip has been added in the middle section of the slot, and antenna-2 is realized, which resonates at 5.8 GHz. Both proposed antennas are tested in free space, while the performance of antenna-2 is investigated for on-body condition. In free space, the measured impedance bandwidths of the antenna are 160 MHz and 210 MHz at 5.5 GHz and 5.8 GHz, respectively. The radiation efficiency of the antenna is 89.4% in free space and 57% on phantom at 5.8 GHz. Both measured and simulated results are observed, and they are in a good agreement.

This paper describes an experimental study of passive intermodulation due to metal-tometal contacts with focus on shape influence. This study investigates PIM value of different contact geometric profiles and different contact areas versus normal forces. A complete description of profiles used is done to achieve a relationship between PIM level and contact shape.

This paper discusses the torque constant density in different types of Double Stator Permanent Magnet Brushless DC Motor (DSPM) which are designed for portable applications. It should have high torque constant density so that it will have higher torque as well as lightweight. Previously, there have been many DSPM motor designs that only focus on increasing the torque constant and torque density. However, it is unclear which DSPM motor is the best since the torque constant and torque density are different parameters. Torque constant density will include the torque, volume and current of the motor. The objective of this research is to analyze different types of DSPM motors including the proposed Slotted Rotor DSPM motor (DSPM-SR) which produces higher torque constant density. Besides that, this paper also describes in detail the torque constant density from an electromagnetic point of view. Finite Element Analysis (FEA) and analytical calculation are used to simulate the characteristic of various double stators. The result shows that DSPM-SR has 90.5% higher back electromotive force (emf) and 87.5% higher torque than DSPM-ST. Besides that, the DSPM-SR topology has higher torque constant density about 67.27% than other DSPM motors. As a conclusion, this paper provides the overview and comparison of torque constant densities of various DSPM motors.

Present paper describes the design, development and evaluation of a wideband, compact Ku-band orthomode transducer (OMT) for SATCOM application. It consists of a square waveguide output section, square waveguide to rectangular waveguide transition, straight waveguide port and an orthogonally coupled port. A tapered waveguide section has been used to couple the orthogonal RF (Radio Frequency) signal to the common port. The designed OMT has a transmit port with frequency band 13.75 GHz-14.5 GHz and a receive port with frequency band 10.95-12.5 GHz. Finite element method based ANSYS's High Frequency Structure Simulator (HFSS) EM software has been used for simulation and optimization of OMT. Measured reflection coefficients of OMT over transmission and reception frequency bands are better than -15 dB and -12 dB, respectively. Designed OMT has port to port isolation better than 45 dB against 30 dB isolation of conventional OMT available in market.

A new approach is presented to reduce the monostatic radar cross section (RCS) of a metal surface. In this approach, called Polarization Cancelation, the polarization of incident wave is rotated by several angles so that the reflected wave becomes zero in direction of incidence. The characteristics and mechanism of the polarization rotation and RCS reduction are investigated. The presented approach is verified by simulation and measurement results.

A two-dimensional Green's function for a half space geometry, comprising planar interface only due to two different non-integer dimensional spaces, has been derived. Medium hosting the time harmonic electric line source and planar interface is homogeneous and isotropic. Radiated field is written in terms of unknown spectrum of plane waves. Unknown spectrum functions are determined using the related boundary conditions. It has been shown that although wavenumbers of both half spaces are same, due to difference of dimensions of the two half spaces, reflection and transmission occur. When dimensions of both half spaces are taken equal to two, derived expressions yield field radiated by a line source in an unbounded homogeneous medium with integer dimensional space.

A symplectic pseudospectral time-domain (SPSTD) scheme is developed to solve Schrodinger equation. Instead of spatial finite differences in conventional finite-difference time-domain (FDTD) methods, fast Fourier transform is used to calculate spatial derivatives. In time domain, the scheme adopts high-order symplectic integrators to simulate time evolution of Schrodinger equation. A detailed numerical study on the eigenvalue problems of 1D quantum well and 3D harmonic oscillator is carried out. The simulation results strongly confirm the advantages of the SPSTD scheme over the traditional PSTD method and FDTD approach. Furthermore, by comparing to the traditional PSTD method and the non-symplectic Runge-Kutta (RK) method, the explicit SPSTD scheme, which is an infinite order of accuracy in space domain and energy-conserving in time domain, is well suited for a long-term simulation.

A variety of techniques are available to reduce cogging torque in Permanent Magnet Brushless DC (PMBLDC) motors. In general, all the techniques are meant for effectively reducing the cogging torque. This paper presents a new technique for cogging torque reduction in a radial flux surface mounted PMBLDC motor by applying the proposed T-shaped bifurcation method in the stator teeth of a PMBLDC motor. The Finite Element Analysis (FEA) is carried out for the T-shaped bifurcation method applied to a PMBLDC motor, and analysis is done using Virtual Work (VW) method. The CAD software package MagNet has been used to completely analyze the T-shaped bifurcation based PMBLDC motor. FEA and CAD simulated results are compared for the reduction of cogging torque values. It is found that the cogging torque reductions in the two methods are nearly the same. The cogging torque and the flux density values of the motor calculated using the proposed T-shaped bifurcation method are compared with the corresponding values of the recently introduced Reduced Stator Slot Width method. The proposed T-shaped bifurcation is very effective compared to the existing techniques in reducing the cogging torque.

A novel dual-layer ultra-wideband lotus-wearable antenna is presented in this paper for integration on astronaut's flight jacket to monitor the vital signs of astronauts. The proposed antenna is designed and fabricated on a leather material as a substrate to operate over a frequency band (2-12 GHz). The dielectric constant ε_r = 1.79 and loss tangent tanδ = 0.042 of the leather material are measured by using two different methods. The proposed antenna has three-strip lines in the 2nd layer for performance enhancement. The stretching effect of the proposed antenna on its impedance characteristics is studied. Furthermore, SAR calculations are performed on-body environments to ensure that operated properly in the nearness of the human body. Finally, the proposed design is simulated by CST simulator version 2016, fabricated using folded copper and measured by Agilent8719ES VNA. The measured results agree well with the simulated ones.

A seven-band antenna for vehicle-mounted T-BOX with a compact structure is proposed and studied. The proposed antenna is composed of a monopole branch and a ground branch. In addition, a slot is embedded in the monopole branch for bandwidth enhancement. By using 0.25- and 0.5-wavelength modes, the lower band (824-960 MHz) and higher band (1710-2690 MHz) are covered. The working mechanism is analyzed based on S-parameters and surface current distributions. The attractive merits of the proposed antenna are that the structure is compact with a small ground, and no lumped element is used. The measured results show that the antenna can cover the lower band of GSM850/900 and the desired upper band of DCS1800/PCS1900/UMTS2100/LTE2300/2500. The measured efficiencies are also presented.

A circular microstrip antenna (CMSA) cannot be fed directly with 50 Ω microstrip (MS) line, without an inset or an impedance transformer, as all around the periphery the impedance is equally high. The feeding technique such as inset fed or quarter wave transformer makes the antenna geometry asymmetrical. In this paper, a technique using single shorting post and a pair of shorting posts is proposed to match the peripheral impedance of the CMSA with that of the 50 Ω-MS-line feed for operation around 2.45 GHz. The shorting posts perturb the current distribution on the patch, altering the input impedance at the periphery. By selecting proper shorting posts positions a wide range of impedance has been adjusted without altering the patch geometry. Due to symmetric arrangement of the double shorting posts, the proposed antenna configuration has a very low cross-polarization ratio of better than -65 dB at the broadside direction for 2.45 GHz. The simulated results of the directly fed 50 Ω-MS-line CMSAs are experimentally validated with good agreement.

A new optimization algorithm for the Cylindrical Polarimetric Phased Array Radar (CPPAR) antenna pattern synthesis is presented to achieve multi-mission requirements. To allow accurate weather measurements, the CPPAR antenna needs to have matched co-polarization (H and V) patterns, low sidelobe levels and high cross-polarization purity. To achieve these goals, first, a high-performance dual-polarized hybrid-fed microstrip patch antenna is designed, and its embedded radiation pattern is extracted. Then, a pattern synthesis using a new optimization method is presented to find the optimal weights for each radiating element and each polarization. The modified particle swarm optimization (MPSO) with new features is used to optimize the current distribution of the CPPAR. The adaptive beamforming algorithm also has the capability to mitigate interference by steering nulls of the radiation pattern in the desired direction without aecting the main beam. The performance improvement is demonstrated through the simulation results.

This paper presents a direction of arrival (DOA) estimation method. Spectral-domain interferometer equation is first established based on integral transforms of spatial interferometer equations. The direction finding problem in the spatial domain is thereby mapped to that in the spectral domain, relating angular parameters to spatial spectrums. This method is then applied to DOA estimation with circular arrays and spherical arrays. As a result, the elevation angle and azimuth angle are decoupled, giving closed-form and analytical formulae for DOA estimations by discrete phase samples on a sampling aperture. Algebraic relations between angular parameters and phase samples are established, and this method is hence computationally efficient. The Cramer-Rao lower bound (CRLB) of the proposed method is derived, and accuracy analysis demonstrates that the proposed method approaches the CRLB. In addition, mathematical insights into accuracy enhancement by large number of samples are observed via Parseval's theorem. Finally, numerical simulations and experimental measurements are provided to verify the effectiveness and appealing performance of the proposed method.

This paper presents the performance of cylindrical plasma antenna. A plasma tube is used as radiating element. The antenna is designed and works at different frequencies. To couple electromagnetic signal from the coaxial probe to the plasma column, a coupling system is realized. It permits to excite the tube in order to have a monopole or dipole antenna. The performances of the cylindrical plasma antenna are given in terms of S₁₁, gain and radiations patterns.

This paper presents the design and evaluation of a compact antenna system with pattern reconfigurability at 2.6 GHz. The antenna is based on the concept of an electronically steerable parasitic array radiator (ESPAR), and its height is reduced by top loading. The antenna can generate 10 reconfigurable patterns with a maximal gain of 7.4 dBi. Furthermore, a multiple antenna system consisting of these antennas is proposed. The radiation patterns realized by this multiple-input-multiple-output (MIMO) system are optimized for automotive urban scenarios based on the results of previous research. The S-parameter measurement results of a fabricated prototype correlate with the simulation. Furthermore, 3D measurements of radiation patterns correspond very well with simulation and gain up to 8 dBi is obtained.

A miniaturized rat-race coupler with arbitrary power division ratio is proposed in this paper. The design formulas of the rat-race coupler with arbitrary power division ratio are derived using the even-odd decomposition analysis. The proposed structure demonstrates miniaturized size and perfect isolation due to adding phase inverter to the branch. For demonstration, a 20 dB rat-race coupler operating at 1 GHz with 81.34% size reduction is designed and fabricated. There is good agreement between measured and simulated results.

We study the electrical conductivity of three-dimensional (3D) nanocomposite with incorporated random carbon nanotubes (CNT). Large length of the remote nanotubes generates a lot of intersections that induce rather small percolating threshold of the global conductivity in this medium. We simulate such a system by random cylinders placed in a percolating parallelepiped with the use of Monte Carlo method. Conductivity of such structure is associated with the critical phenomena, where the main transition parameter is dened by the value of the percolation threshold. We calculate the minimal percolating threshold and determine the functional form of the conductivity by the global optimization technique. Such an approach allows studying the details of the electrical conductivity in nanocomposites even at signicant level of the percolating fluctuations.

The main objective of this article is to design, realize and measure the performance of a reconfigurable antenna for wireless applications. The designed antenna will be able to switch among several modes, from the ultra-wideband mode (UWB mode) to narrow band mode (NB mode) and then dual-band mode (Bi-bands mode) and vice versa in order to combine the maximum functionality. By incorporating two resonators into the octagonal antenna, the initial antenna can be covered by one wideband (UWB mode), one narrow sub-band (NB mode), or two narrow sub-bands (Bi-bands mode). The ultra-wideband mode is obtained by deactivating the two resonators (so the antenna operates as a classical octagonal antenna), while the one narrow band mode is obtained by activating just one resonator. In the bi-bands mode, the two resonators are activated at a time to be used as a coupling-bridge to very narrow frequency bands. To present the work, simulated and measured results are given and discussed.

We present a new equal power quadrature branch line coupler (BLC) for dual-band applications in this paper. A new topology of the dual-band quarter wavelength transmission lines (TL) with the derivation of design equations is also introduced. The proposed BLC is designed using Advanced Design System (ADS) and fabricated on Rogers 5870 at 0.9 GHz and 2.4 GHz center frequencies. The design approach for the proposed dual-band BLC is endorsed by the simulated and measured results. A comparative analysis of this BLC with the previous BLCs is also carried out.