General design guidelines for unidirectional electrically small parasitic array has been proposed by several researchers; however, the input resistance of these antennas is normally very low. In order to practically ``transfer'' this high directivity into realized gain, an appropriate matching mechanism is necessary. This paper gives a simple matching method by adding an inductive stub close to the antenna feed, which can effectively increase the antenna input impedance to 50 Ω and keep the gain almost invariant. Besides, it could make the resonant frequency very close to the frequency where maximum gain occurs, thus a high realized gain can be achieved. Computed and measured examples are given to validate this method.

This paper presents a narrow-band bandpass filter (NBBPF) using three cylindrical dielectric resonators (CDRs) placed on three rectangular metallic cavities (RMCs). Two U-shaped planar resonators located between RMCs are used to realize narrow-band response effectively. The 3 dB fractional bandwidth (FBW) of the proposed filter is 0.275%. The filter is designed for X-band (9.85 GHz), with 20 MHz bandwidth for radar, satellite, and medical accelerators applications. High Q-factor (Q-factor = 400) and low fabrication cost are other advantages of the proposed design. The proposed NBBPF was fabricated, and its performance was measured to verify the design. Good agreement between the measured and simulated data is obtained.

In this paper, a novel broadband circular polarized (CP) antenna for mobile communication is proposed. The antenna is constructed as a square ring with a gap and coplanar waveguide (CPW) feed. To achieve a broadband CP wave, a cross patch is embedded at the center of the slotted square ring to excite two orthogonal resonant modes with equal amplitude and 90° phase difference for CP radiation. Furthermore, on one side of ground a stub is embedded to match impedance bandwidth that can cover the whole CP bandwidth completely. Loading the AMC (Artificial magnetic conductor) structure on the back of the antenna achieves unidirectional radiation of circular polarized waves. An antenna was fabricated based on simulation and optimization. The simulated and measured results show that the bandwidth with S₁₁<-10 dB is 66.9% from 1.82 GHz to 3.65 GHz, and the 3 dB axial ratio bandwidth is 52.8% from 1.95 GHz~3.35 GHz.

The electromagnetic characteristics of a high speed IC power distribution network (PDN) are of vital important with the rapid increasing of operation speed and scale down CMOS manufacturing size, in particular, the fundamental electromagnetic theory including impedance and loop inductance of various designed IC power-plane structures. In addition, the area occupancy ratio of slot (AOROS) of irregular parallel-plane structures with multi-slots plays a key role in PDN impedance and loop inductance, where the influence of AOROS on impedance and loop inductance is investigated for various structures. Moreover, experimental work is carried out to validate the influence of AOROS on impedance and loop inductance of the PDN. The simulation and measurement of impedance are performed up to 10 GHz, and a good agreement is obtained between the simulation and experiment.

This paper proposes a novel clip-shaped meander-line resonator (CSMLR) to realize miniaturized ultra-narrowband (UNB) bandpass filter design. The main advantage is that it can achieve very weak coupling between adjacent resonators with keeping them very close and introduce transmission zeros (TZs). To further demonstrate the feasibility of using this configuration, a six-pole UNB filter with a fractional bandwidth (FWB) of 0.20% at the center frequency of 1915 MHz was designed on double-sided YBCO high temperature superconducting (HTS) thin films with a thickness of 0.5 mm and dielectric constant of 9.8 by using CSMLR. The measured responses agree rather well with the simulated ones. The measured results show a maximum insertion loss of 0.31 dB and return loss of 15.5 dB in the passband. Two transmission zeroes (TZs) are generated to improve the passband selectivity, which causes the band-edge steepness better than 50 dB/MHz in both transition bands.

Developed initially for military applications, radar technology is rapidly spreading to areas as diverse as natural resource monitoring, civil infrastructure assessment, and homeland security. Waveform design is a critical component to extract maximum information about the targets or features being probed. Waveforms derived from noiselets, one of the family functions of wavelets, can be advantageous in certain applications owing to their random and uncorrelated properties. In this work, radio frequency (RF) noiselet waveforms are introduced and their performance related to detection of arbitrary target interfaces using the cross-correlation method, a form of matched filtering, is assessed. The application of the RF noiselet waveform for nondestructive testing (NDT) of the multilayered dielectric structures is discussed. The application of wideband noiselet waveforms for multiresolution analysis (MRA) is demonstrated.

In this paper design of a stacked circular patch antenna is presented for high gain and wideband applications. The main radiator of this design is a circular patch antenna, which is fed by using a coupling mechanism. Wide impedance bandwidth of 40% and linear polarization of gain 9.5 dBi at the center frequency of 2.4 GHz is measured. The antenna gain is further increased by using regular period of N circular patch directors on top of the main radiator. The first director is placed in a distance of about one half of the wavelength and the next directors are placed with regular distances of about a quarter of the wavelength. The antenna gain is tuned and increased with the number of the directors in the range of 9.5-16.5 dBi with N up to seventeen. The antenna impedance change due to the added directors is adjusted by using two parasitic circular patches between the main radiator and the first director. A prototype antenna is designed, manufactured and measured. The antenna operation can be further extended using dual feed geometry in which we can obtain two orthogonal radiation patterns or circular polarizations.

A design of a half-mode substrate integrated waveguide (HMSIW) cavity-backed self-diplexing antenna is proposed with a two-layer structure. The top layer comprises two HMSIW based cavities, and radiating patches are etched on the top-cladding of each cavity. The radiating patches are excited by two distinct printed microstrip lines on the backside of the bottom layer by using shorting-pins. The shorting-pin excites the corresponding cavity in its dominant mode, which resonates at two different frequencies in X-band. The simulated results demonstrate that the proposed design resonates at 8.20 GHz and 10.55 GHz with an isolation of higher than -25 dB between two excitations, which helps to introduce the self-diplexing phenomenon. Also, both resonant frequencies can be tuned independently by varying the dimensions of the corresponding cavity. Moreover, HMSIW cavity-backed structure and proposed feeding technique reduce the overall size of the antenna significantly, while it maintains high gain and unidirectional radiation characteristics for both operating frequencies.

The Meissner effect is studied by using an approach based on Newton and Maxwell's equations. The objective is to assess the relevance of London's equation and shed light on the connection between the Meissner and skin effects. The properties of a superconducting cylinder, cooled in a magnetic field, are accounted for within the same framework. The radial Hall effect is predicted. The energy, associated with the Meissner effect, is calculated and compared with the binding energy of the superconducting phase with respect to the normal one.

This paper presents an imaging radar system for structural health monitoring (SHM) of wind turbine blades. The imaging radar system developed here is based on two frequency modulated continuous wave (FMCW) radar sensors with a high output power of 30 dBm. They have been developed for the frequency bands of 24,05 GHz-24,25 GHz and 33.4 GHz-36.0 GHz, respectively. Following the successful proof of damage detection and localization in laboratory conditions, we present here the installation of the sensor system at the tower of a 2 MW wind energy plant at 95 m above ground. The realization of the SHM-system will be introduced including the sensor system, the data acquisition framework and the signal processing procedures. We have achieved an imaging of the rotor blades using inverse synthetic aperture radar techniques under changing environmental and operational condition. On top of that, it was demonstrated that the front wall and back wall radar echo can be extracted from the measured signals demonstrating the full penetration of wind turbine blades during operation.

This work presents an enhanced rectenna with a differential source feeding scheme for radio frequency (RF) energy harvesting at 2.45 GHz frequency. A circularly polarized (CP) microstrip antenna with embedded slots is designed which efficiently attains harmonics suppression. By modifying size and position of two diametrically opposite triangular projections in the top patch, two orthogonal modes that have equal magnitude and are in phase quadrature are excited. The four radial slots embedded in the antenna can block 2nd and 3rd harmonics which is suitable for onboard rectenna design without harmonics filter. A microstrip tapered feed line is used to match antenna element with 50-ohm impedance. The designed antenna is then tested for RF energy harvesting in two ways. One is conventional single source fed rectenna (SSFR), and the other is proposed differential source fed rectenna (DSFR). In the DSFR, the designed antennas are differentially operated by making a difference of λg/2 path length (λg Guided wavelength), and the ports are then connected to a differentially driven optimized rectifier circuit. For comparison, an SSFR and a DSFR are fabricated and tested. The circuit parameters in each case are optimized in Agilent Design System (ADS) 2011 software to maximize RF to direct current (DC) conversion efficiency. The proposed DSFR has a maximum efficiency (RF-DC) of 41.63% at 10 dBm RF input power. In the input power range from -20 dBm to 10 dBm, the DSFR has improved performance and higher efficiency over the SSFR.

A small size dielectric image line (DIL)-based leaky wave antenna (LWA) is proposed in this paper. Three H-shaped patches as radiation elements are periodically printed on top surface of DIL, which generates infinite higher order space harmonics, and the proposed antenna works at the first order mode. The H-shaped unit cell has high attenuation constant, which leads to power leaking quickly. So high radiation efficiency can be realized with only 3 unit cells. Simultaneously, the open stopband (OSB) is suppressed using H-shaped unit cells to get high efficiency at broadside. The working principle of the proposed antenna is analyzed, and the numerical results validate the theory analysis. Over the operating band (11.5~14.6 GHz), the proposed antenna covers 71° from -41° to 30° (including the broadside) with stable gain (8.7 dBi~10.6 dBi) varying less than 2 dBi. A prototype is fabricated and measured, which have good agreement with simulation results.

A miniaturized ultra-wideband (UWB) antenna based on Sierpinski square slots is reported. The antenna has a compact dimension of only 0.32λ_l×0.32λ_l (28×28 mm²), at a lower frequency of 3.4 GHz. Antenna miniaturization is achieved by etching Sierpinski square slots in the radiating decagonal shaped monopole, and UWB operations are accomplished by utilizing double truncations in the ground plane. The designed antenna has a fractional bandwidth of about 127.3% (3.41-15.37 GHz) in simulation and about 124.7% (3.50-15.1 GHz) in measurement. The time domain characteristics of the designed antenna are discussed in detail. Good radiation characteristics and impedance matching are exhibited by the designed fractal antenna in the entire UWB range.

In this paper, a very compact 6.1GHz band notched printed multiple-input multiple output (MIMO) antenna with the size of only 25×25 mm² is presented for Ultra-wideband (UWB) applications. Two symmetrical antenna elements are placed in vertical direction which make it easy to realize good diversity performance. The antenna elements are made up of a microstrip feed line and rounded patch. One slit is in the diagonal position, and one slot line is designed to improve the isolation between two orthogonal antenna elements. The 6.1 GHz band notch weakens the probable interference between C band satellite uplink communications and UWB system. Simulated and measured results show that it covers from 3.1 to 12 GHz with S₁₁<-10 dB except rejected band, and the isolation is better than 15 dB in full UWB spectrum.

Within the framework of the higher-order Kirchhoff approximation, the properties of the electromagnetic scattering from sinusoidal water waves are presented, and the theoretical formulas up to third-order for describing the scattering field and its spectrum are derived. It shows that not only the spectral peaks which correspond to phase velocity of the water wave but also other discrete harmonic peaks can be found from the theoretical spectrum model. And the Doppler shifts of the spectral peaks are all integral multiple of the sinusoidal wave's frequency. For the backscattering field from a sinusoidal wave, the higher-order resonant peaks would also be found at different scattering angles, and the values of these peaks decrease with the scattering angle. On the other hand, the comparisons with the MoM demonstrate that the contributions of the slope-dependent terms can be generally neglected if the amplitude of the sinusoidal wave is small. However, if the waves slope is larger, the impact of the second order scattering becomes obvious and cannot be omitted.

The joint direction-of-arrival (DOA) and frequency estimation problem has received significant attention recently in some applications, including pulsed Doppler radar, multipath parameter estimation, etc. This paper presents a novel virtual space-frequency matrix method to estimate the DOA and frequency jointly. Via the temporal smoothing technique, a virtual space-frequency matrix is defined, which includes the information of the incident DOAs and the frequencies. Making using of the proposed method, both the frequencies and DOAs can be estimated by eigenvalues and the corresponding eigenvectors of the new defined virtual space-frequency matrix, respectively. Therefore, the pairing of the estimated DOAs and frequencies is automatically determined. Compared with related works, the proposed method can provide superior performance, such as higher estimation accuracy, without the procedure of parameter search or parameter matching. Simulation results are presented to demonstrate the efficacy of the proposed approach.

A single-fed compact circularly polarized quarter-mode substrate integrated waveguide (QMSIW) antenna with improved bandwidth is designed based on a single-layer structure. The antenna consists of four QMSIW elements. Instead of using a complex power divider to excite each element, an inset microstrip line is employed to excite the driven QMSIW element, while the parasitic QMSIW elements are excited by means of gap and direct couplings. Moreover, the phase and magnitude of the electromagnetic fields in each QMSIW element are controlled by gaps and short sections of microstrip line to obtain a circularly polarized radiation. A prototype of the proposed antenna is fabricated and measured, and the measured results are in good agreement with the simulated ones. The measured 10-dB impedance bandwidth is 6.23%, from 5.13 GHz to 5.46 GHz, and the 3-dB axial-ratio bandwidth is 3.62%, from 5.15 GHz to 5.34 GHz. The measured maximum gain of the antenna is 6.46 dBic.

To achieve radial suspension and eliminate the effect of rotor gravity in wind turbines, a novel structure of a generator combined with a magnetic bearing (GCWMB) is proposed in this paper. The GCWMB not only has the characteristics of the traditional permanent magnet (PM) generator but also has the advantages of reducing friction and starting wind speed, eliminating rotor gravity. The structure and principle of the GCWMB are analyzed in this paper. To improve the calculation accuracy of flux density, an analytical model based on the Fourier series decomposition is proposed to establish the model of flux density in the outer air gap. Taking into account the edge effects and the eccentricity of the rotor, an improved equivalent magnetic circuit method is adopted to model and analyze the flux density in the inner air gap. The effectiveness and correctness of the proposed analytical model in the outer and inner air gaps are verified by finite element analysis (FEA) and experiments.

This paper aims to study the plasma discharge process of a 5 kW hall thruster developed by Lanzhou Institute of Physics and to provide the knowledge for implementing an improved thruster design. A 2D Particle-In-Cell (PIC) model is built, in which the electron-electron and electron-ion Coulomb collisions are included, in addition to the elastic, excitation, and ionization collisions between electrons and neutral atoms, and the elastic and charge-collisions between ions and neutral atoms. Different Bohm diffusion coefficients are applied in different regions to simulate the Bohm diffusion. The deviation between the simulated and experimental results of the thruster performance is within 15%, validating the accuracy of the model indirectly. The discharge process including the transient and steady-state oscillations is well reproduced. The character of the plasma during different phase of the discharge process including the plasma density and ionization rate is simulated and analyzed. Finally, the probable factor causing the anode erosion is determined.

Due to a recent growth in three-dimension (3D) printing technology, engineers can fabricate affordable and versatile antennas; however, lossy conductive materials, inadequate antenna terminations, and simplistic designs which do not adequately utilize the available volume continue to limit the capabilities of 3D printed antennas. In this work, the dielectric constants of three polylactic acid (PLA) materials, dielectric PLA, magnetic PLA and conductive PLA, were measured using the coaxial transmission line method, and the results were compared with measurements using the commercially available coaxial probe method. Based on published dielectric constants for solid non-printed PLA, a variety of antenna designs were simulated and fabricated. Each of these antenna designs addressed a certain shortcoming faced by 3D printed antennas. The antennas were designed with a target resonant frequency of 2.45 GHz, an impedance bandwidth of at least 500 MHz, and a gain greater than 1.5 dBi. The three antennas presented here are a fractal bow-tie antenna (FBTA), a spiral antenna, and a Yagi-Uda antenna.