A compact microstrip Rotman lens is proposed in this paper. The microstrip Rotman lens consists of a lens body and Chebyshev impedance transformers. The Chebyshev impedance transformers are used as beam ports, array ports and dummy ports. Compared to the traditional linear tapered transition, the Chebyshev impedance transformer is shorter, which leads to the size reduction and insertion loss improvement for the Rotman lens. An X-band 4×7 Rotman lens using Chebyshev impedance transformers is designed and fabricated. Compared to a traditional Rotman lens, the proposed Rotman lens shows a size reduction of about 56% and an insertion loss improvement at 10 GHz. The measured results demonstrate that better than 15 dB return loss throughout the bandwidth from 8 to 12 GHz is obtained.

Due to urgent needs for exploring new energy resources, a novel approach is developed in this paper to integrate the functions of a photovoltaic (PV) panel with an ultra-wide band (UWB) antenna array as a unit for collecting solar energy and RF radiation power. The UWB antenna is printed on the front panel of the PV surface. The antenna structure is customized with minimum shadowing effects on the PV surface, by using eight monopoles connected to one SMA port as a single antenna array. Then, to ensure the bandwidth enhancement, each monopole is coupled to three Split Ring Resonators (SRR) structured in a single column as a matching circuit. Next, an experimental study is performed to investigate the amount of the harvested energy from both the PV and the antenna array. The antenna experimental measurements are conducted to realize the I-V characteristics for the PV and produced output voltage and efficiency from the RF radiation power at 900 MHz only. Numerically, the proposed antenna array performance is simulated by CST MWS and HFSS software packages. Finally, the antenna performance in terms of S₁₁ and the radiation pattern at 900 MHz are measured and compared to the simulated results to end up with excellent agreements.

Polyomino-based arrays allow to efficiently exploit the available array area with a regular element lattice, yet exhibit a non-uniform distribution of their phase centers, leading to superior electronic scanning capabilities. Yet polyomino arrays are usually implemented via polyomino of equal order, leading to uniform amplitude distribution and poor side lobe levels. In this contribution, a tiling of polyominoes of different order is proposed to attain at the same time good scanning characteristics and side lobe level.

In this paper, we propose a novel direction of arrival (DOA) and polarization estimation method to address the problem of a coprime polarization-sensitive array (PSA). For a PSA, there may be a zero element in the covariance matrix when the polarized signal comes from a specific direction. To overcome this problem, we utilize the reconstructed received data to obtain a new covariance matrix whose elements are all non-zero. Then, the coprime MUSIC and sparse signal reconstruction algorithms are used for DOA estimation. In addition, the power of noise can be estimated in this polarization model, which improves upon the sparse signal reconstruction algorithm. Compared with the normalized algorithm, the proposed method offers favorable performance in terms of accuracy. Furthermore, our method can identify the peaks of the true DOAs at a low signal-to-noise ratio (SNR). The simulation results demonstrate the effectiveness of the proposed method.

The Lienard-Wichert potentials show that radiation is caused by charge acceleration. The question arises about where charge acceleration occurs on the most basic of antennas, a center-fed, perfectly conducting dipole, for which there are two obvious causes. One is the feeedpoint exciting voltage that sets into motion an outward-propagating charge and current wave at light speed c in the medium. A second is at the dipole ends where the outgoing wave is totally reflected producing a change in charge speed of 2c. A third is the decreasing amplitude of the propagating wave with distance due to its partial reflection along the wire. That reflected charge also undergoes a speed change of 2c. This is the reason why the decay of current flowing along a straight wire antenna has been attributed as being due to radiation. Radiation caused by these and other kinds of charge acceleration due to resistive loads, right-angle bends, and radius steps are investigated. These phenomena are examined primarily in the time-domain where they are more observably separable in time and space than in the frequency domain. The current and charge induced on an impulsively excited wire antenna and its broadside radiated E-field are computed using a time-domain, integral-equation model. The computed results are used to derive a numerical relationship between the amount of accelerated charge and its radiated field. This relationship is denoted as an Acceleration Factor (AF) that is obtained for various charge-accelerating features of a generic wire object are normalized to that of the exciting source for comparison with their respect speed changes.

Investigation of backscattering enhancement of waves propagation in random medium is a crucial factor in remote sensing. Medium effects on waves backscattering are important to measure the error rate in radar detection of targets with a finite size. In this paper, we present numerical results for the backscattering enhancement factor assuming different medium parameters and target configuration. Convex illumination region of partially convex surface is assumed. We consider targets to take large sizes of about five wavelengths and a plane wave incidence in the far field. Waves propagation and scattering from objects are calculated in free space and random medium while considering Epolarization of incident wave.

This paper provides the theoretical validation of the unconditional stability, using the Von Neumann method, for the radial point interpolation method (RPIM) and Crank-Nicolson (CN) scheme, in a three dimensional (3D) problem. Moreover, the matrix inversion process, typical of the CN implicit scheme, is circumvented and approximated by a finite series for a particular stability factor range. To validate numerically the efficiency of the CN-RPIM unconditional stability, the resonant frequency inside a 2D double ridged rectangular cavity is simulated. The numerical results confirm that the CN-RPIM is significantly efficient, since the simulation time is reduced by up to 90%, and the memory requirement is saved up to 81%, with a few loss of accuracy.

The work presents an inventive, simple and implementable design approach to enhance the bandwidth of conventional Salisbury Screen Microwave Absorber (SSMA). Theoretically, the maximum fractional bandwidth of SSMA for FR4 substrate with an optimum sheet resistivity of 308 Ω/sq for -10 dB reflection is nearly 42.1%. In comparison, the bandwidth for square patch based SSMA is 59.7% with the same thickness. The design comprises square patches of SSMA placed periodically on a metal sheet. The square patches consist of an FR4 substrate and a 200 Ω/sq resistive sheet. A single reflection null is observed in the SSMA due to λ/4 resonance whereas in the proposed absorber an additional resonant mode is introduced due to coupling between the nearby patches. The simultaneous overlapping of the λ/4 mode and the additional coupling mode results in bandwidth extension. The close agreement between the simulation and measurement data is observed.

High power density and torque capability are distinguished features of slotted axial flux permanent magnet machine. However, due to alternate placement of slot and teeth, the airgap permeance and airgap magnetic energy vary with angular position. Even in absence of current excitation, the magnetic variation with position results in cogging torque. This torque produces several undesirable phenomena such as mechanical vibration, acoustic noise, torque ripples, voltage ripples and speed ripple in machine performance. The severity is high for low speed, light load, and direct drive applications. Various design modifications such as slot skewing, magnet skewing, axillary slots, optimization of pole pitch to pole arc ratio and many more are reported for cogging torque mitigation. Any of these design modifications adversely affects the machine performance in terms of no load magnetic field distribution, linkage flux, and induced emf. In this paper, the effect of magnet skewing is investigated for dual-rotor permanent magnet axial flux machine. The analytical model is developed for the determination of magnetic field distribution at no load. Three different types of open slots stators viz. type 1: trapezoidal Slot with trapezoidal teeth, type 2: Parallel slot with trapezoidal teeth, and type 3: trapezoidal slot with parallel teeth are used for the investigation of air-gap magnetic field density and cogging torque produced in machine. The analytically obtained results are compared with finite element analysis (FEA) for the validation.

Statistical characteristics of scattered ordinary and extraordinary electromagnetic waves in the magnetized plasma are considered using the smooth perturbation method. Diffraction effects and polarization coefficients are taken into account. Second order statistical moments of scattered radiation are obtained for arbitrary correlation function of electron density fluctuations. The expressions of the broadening of the spatial power spectrum and displacement of its maximum are obtained. Wave structure functions and the angle of arrivals are calculated. Scintillation level of scattered radiation is analyzed for different parameters characterizing anisotropic plasma irregularities for the ionospheric F-region. Numerical calculations of the statistical characteristics are carried out for the three-dimensional spectral function containing anisotropic Gaussian and power-law spectral functions using the experimental data.

In this paper, we propose a novel compact switchable monopole CPW-fed antenna which has the ability to be used for narrowband as well as UWB applications. A single element antenna to be used for wireless local area network (WLAN) applications is first proposed in this article having overall dimensions of 24×30.5 mm². The corresponding antenna has been transformed to UWB frequency range just by utilizing two variable capacitors within the designed structure. The proposed small size, variable, low cost as well as low weight antenna with good propagation characteristics performs well in the WLAN as well as in the UWB frequency band. The proposed antennais simulated using Ansoft HFSS, and results are validated in CST Microwave Studio suite. The proposed antenna has also been fabricated, and the measured response is correlated with the simulated ones.

The paper presents the results of observing, in a real time, the process of combustion in air of aluminum nanopowder ignited by laser radiation. The obtained results convincingly evidence the possibility and perspective of visualization of ignition process by means of laser monitor. The video images allow observing the main stages of the combustion process including starting of combustion in the place of laser radiation focusing, spreading of the heat wave and appearance of the second combustion wave. For quantitative analysis of the combustion process, we suggest to analyze the average intensity of images registered by laser monitor.

A low phase noise reflection oscillator using a hexagonal substrate integrated waveguide (SIW) resonator is proposed in this paper. The hexagonal SIW resonator, which can combine flexibility of a rectangular cavity and performance of a circular cavity, is convenient for oscillator design. Since any of the six sides of a hexagonal resonator can be utilized for coupling, the oscillator configuration is flexible and adaptable. A simplified generalised phase noise condition and its optimization approach are proposed for the low-phase noise oscillator design. Furthermore, a 10.4 GHz oscillator prototype was designed, fabricated and measured to validate the proposed optimization approach. The measured results show that this oscillator provides 11.3 dBm output power and possesses low phase noise of -127.2 dBc/Hz at 1 MHz offset from 10.4 GHz carrier frequency, which is suitable for low-cost application in microwave and millimeter-wave band.

This paper presents a comprehensive analysis of a current-mode-logic frequency divider (CML FD) and the theoretical locking range of CML FD. The locking range of the CML divider is proportional to the injection ratio. By adding a resistive load, the locking range of the CML divider is not limited by the Q value of the LC resonant circuit. The minimum input power to drive the divider is achieved when the output frequency is equal to the self-oscillation frequency. To verify the properties of wideband and multi-phase outputs, the ÷4 octet-phase frequency divider based on a two-stage CML FD was implemented using a 0.18 μm CMOS process. It has a locking range of 1 GHz to 8 GHz with a 12.6 mW dc power consumption, and the phase deviation between the octet output signals is less than 4.7°. With an ultra-wide frequency bandwidth and accurate octet outputs, the proposed divider is suitable for multi-phase generator applications.

In this paper, the effect of corrosion on the magnetic behavior of a magnetic material used as a magnetic circuit in the induction machines is studied. With this objective, the magnetic properties of the samples with corrosion and without corrosion were evaluated by the study of hysteresis loops using a homemade vibrating sample magnetometer (VSM). The magnetic parameters extracted from the hysteresis loops such as saturation magnetization, coercive, remanent magnetization, squareness ratio, magnetic permeability, and hysteresis area were analyzed. It was shown that more energy is required to demagnetize the sample with corrosion than the sample without corrosion, and the hysteresis loss in the case of the sample with corrosion is more than the case of the sample without corrosion. These mean that when the corrosion is presented in the magnetic circuits of the induction machine, the hysteresis loss increases, consequentially reducing the machine efficiency.

In this paper, a compact dual-band MIMO antenna for WI-MAX and WLAN applications with improved isolation is proposed. The proposed design consists of two counter facing F shaped monopoles placed closely to each other with edge to edge spacing of 10 mm (0.1167λ₀ at 3.5 GHz). Each monopole element operates over 3.5 and 5.8 GHz bands. The isolation over the operating dual bands is achieved by using an elliptical slot and a rectangular parasitic strip. S₁₁ < -10 dB is achieved over 3.2-3.8 GHz and 5.7-6.2 GHz with S₁₂ < -20 dB. The overall dimension of the proposed antenna is 30 × 26 mm². The proposed antenna has correlation coefficient < 0.03, diversity gain > 9.8 dB with stable radiation pattern over the operating dual bands. The measured results are in good agreement with the simulated ones. The proposed antenna is a suitable candidate for MIMO applications.

A pair of broadband double-sided parallel-strip line (DSPSL) to coplanar waveguide (CPW) vertical transitions are presented. The transitions are composed of CPW open end with connected grounds forming two strips of the DSPSL with single via connection. The connected grounds of CPW, which forms top strip of the DSPSL are of two dierent shapes resulting in two transitions (Types 1 & 2). Simulated results for the back-to-back transitions, using the multilayer solver of CST Microwave Studio, show good agreement with the measured ones.

As a kind of complex targets, the non-rigid vibration of an aircraft as well as its attitude change and the rotation of its rotating parts will induce complex nonlinear modulation on its echo from low-resolution radars. If these nonlinear modulation features which reflect the physical characteristics of an aircraft target can be extracted effectively, then they are helpful to target classification and recognition. However, the echo translational component and background clutter have a very adverse effect on the extraction of such features. On basis of introducing the ensemble empirical mode decomposition (EEMD) algorithm, the paper firstly performs the decomposition of real recorded aircraft echo data from a low-resolution radar by EEMD and distinguishes the false component, body translational component and micro-motion component by calculating waveform entropy in the Doppler domain. Secondly, it carries out characteristic analysis and feature extraction further on the echo micro-motion component separated and extracts three features of the micro-motion component, including Doppler domain waveform entropy E_mc, normalized equivalent Doppler spectrum width BW₀, and normalized frequency interval between the adjacent maximum spectral peaks on both sides of the spectrum center Δf₀. The analysis results show that EEMD can be used to separate the body translational component and micromotion component of an aircraft echo effectively, and the proposed features (E_mc, BW₀ and Δf₀) can be used as effective features for aircraft target classification and recognition.

A modified three-way in-phase equal Gysel power divider/combiner (PDC) and a method for implementation this novel three-way Gysel PDC on plane structure are proposed in this article. To obtain accurate values of the line impedance,the derivation of the exact equations is based on even-odd mode analysis. An experimental prototype is realized. The results show that this three-way Gysel PDC has good matching, isolation and magnitude-phase balances with high power handling capabilities.

This paper presents a novel 2D meta-surface wall to increase the isolation between microstrip patch radiators in an antenna array that is operating in the teraherz (THz) band of 139-141 GHz for applications including communications, medical and security screening systems. The meta-surface unit-cell comprises conjoined twin `Y-shape' microstrip structures, which are inter-digitally interleaved together to create the meta-surface wall. The proposed meta-surface wall is free of via holes and defected ground-plane hence easing its fabrication. The meta-surface wall is inserted tightly between the radiating elements to reduce surface wave mutual coupling. For best isolation performance the wall is oriented orthogonal to the patch antennas. The antenna array exhibits a gain of 9.0 dBi with high isolation level of less than -63 dB between transmit and receive antennas in the specified THz-band. The proposed technique achieves mutual coupling suppression of more than 10 dB over a much wider frequency bandwidth (2 GHz) than achieved to date. With the proposed technique the edge-to-edge gap between the transmit and receive patch antennas can be reduced to 2.5 mm. Dimensions of the transmit and receive patch antennas are 5×5 mm² with ground-plane size of 9×4.25 mm² when being constructed on a conventional lossy substrate with thickness of 1.6 mm.