This paper presents a P-OMP-IR algorithm for the hybrid precoding problem in millimeter wave (mm-Wave) multiple-input multiple-output (MIMO) systems. In the proposed approach, the digital precoding matrix is updated via the orthogonal matching pursuit (OMP) method, and the analog precoding matrix is refined column by column using the dominant singular value and corresponding singular vectors of a residual matrix successively. During the refining phase of the analog precoding matrix, an extended power method is designed to calculate the dominant singular value and the corresponding left and right singular vectors, which is able to reduce the computational complexity significantly. Simulation results show that the proposed algorithm can not only reduce the residual of the hybrid precoder effectively, but also improve the spectral efficiency consistently.

In this paper, a dual-band complementary split ring resonator (C-SRR) is used to improve the band-notch effect relative to the traditional SRR. Meanwhile, we employ a brand-new SRR unit cell as an isolator for decoupling among multiple bands without enlarging the dimensions of the multiple-input-multiple-output (MIMO) antenna. Therefore, a compact ultra-wideband MIMO antenna is developed. Compared with the previous work, the proposed MIMO antenna also has obvious advantages such as high isolation and miniaturization (the dimensions are only 13.5 mm × 34 mm). The metamaterial-inspired UWB MIMO antenna presented here is suitable for small scaled mobile devices.

In this paper, an ultra-wideband standard transducer based on microstrip line is developed for the accurate measurement and metrology of UWB-SP. The transducer consists of a section of microstrip line and a section of coaxial line connected to microstrip line via an SMA connector. The beginning end of the transducer is chosen to receive the excitation signal, to expand the effective time window. Simulated results show that the waveform recovered by the transducer is almost coincident with the excited electric field waveform within the effective time window, and the upper frequency of the bandwidth is up to 3.5 GHz. The measured results show that the transducer can recover the waveform of the incident electric field very well, the sensitivity and time window can be calibrated readily and accurately by and the vector network analyzer as well as the UWB TEM cell. The experimental results are in agreement with the results from theoretical results and simulated results.

A novel characterization method of OTA test setups for wireless communication systems on vehicles in the random line-of-sight (Random-LOS) environment is proposed. The measurement setup assumes a compact range and a test zone where the antenna under test (AUT) on the vehicle would be located. An ideal receiver is assumed for the reference measurement, which allows to perform a system analysis through evaluating the Probability of Detection (PoD) as the system figure-of-merit. The proposed method is aimed as an aid for test equipment designers to design OTA compact ranges, compare their performances, and define an ideal numerical reference. The requirements for OTA measurement ranges are different from those for conventional anechoic compact ranges. A compact cylindrical reflector system with an antenna array line feed is characterized using the proposed method, from 1.6-2.7 GHz, for two orthogonal polarizations, various AUT heights and reflector tilting angles, with and without ground plane in a test zone which is 2 m wide in diameter.

In order to solve a key issue about power and data wireless transmission of implantable medical devices, M-ary differentially-encoded amplitude and phase-shift Keying (MDAPSK) is employed to balance the frequency selective contradiction in this paper. Subsequently, bio-capacitor model and biological path loss model are introduced to improve the accuracy of conventional wireless power transmission efficiency model. Based on 16DAPSK modulation, biological channel error rate analysis model is set up. Compared with experiment data, accuracy of the model is proved. Error codes suppression and error codes correction methods are optimized, and the optimization results have been verified by experiments. Lastly, it can be found that the power and data synchronized wireless transmission scheme is feasible. This work provides a new solution and model reference for power and data wireless transmission of implantable medical devices.

Unlike conventional systems in which two identical resonant loops are employed, a pair of novel planar loops is developed for wireless power transfer. The proposed transmitting and receiving coils have different distances between turns while the wire length is the same. The effect of mutual inductance on transfer efficiency is analyzed. The mutual inductance of the proposed loops is more uniform than the conventional one, which is helpful for suppressing frequency splitting at closer transfer distance. Moreover, the power transfer performance is enhanced at longer distance. Additionally, an experimental prototype is fabricated to verify the distance insensitive characteristic of the proposed system.

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.