A simple broadband circularly polarized (CP) aperture antenna is proposed in this letter. The antenna is composed of an L-shaped feed line and a circular aperture. With the newly introduced perturbation slots, a new resonant mode TE₃₁ is generated, which can widen the CP bandwidth without increasing the antenna size. Measured results of the fabricated antenna shows 93.5% (2.9-8 GHz) impedance bandwidth (|S₁₁|<-10 dB) and 66.6% (3-6 GHz) 3 dB axial-ratio bandwidth. The overlapped CP working band covers the entire WiMAX, WLAN and lower frequency 5G bands. Its peak gain is 4.9 dBic at 3.5 GHz, and its gain variation is less than 1 dBic within 3-5.8 GHz band. Design considerations, empirical formulas and surface current analysis are also presented and discussed.

Structural buildings are vulnerable to many types of damages that can occur through their life period. These damages may cause structure failure or at least decrease its efficiency. Dangerous damages occurring in concrete structures are surface opening cracks or sub-surface cracks. So, the determination of location of these cracks is very important, because the crack location is one of the important factors that affect the degree of danger of the damage. The Rayleigh waves have many advantages, as they can be easily recognized due to the maximum energy of the wave components. So, it was used to determine the crack location in the previous works. In this paper, two different techniques are used to determine the crack location; one of them depends on the healthy case, and the other deals only with the cracked case. Common finite element software (Abaqus) is used to model the numerical simulation, and the experimental test is also performed to verify the obtained numerical results. Good agreement between the simulated and experimental results is obtained by employing both techniques to find the crack location.

In present scenario, this paper intends to demonstrate the practicality of a miniaturized coplanar waveguide fed metamaterial inspired antenna that can be effectively operated at dual bands. A broad-side coupled Split Ring Resonator is used to obtain dual bands with an impedance bandwidth (-10 dB) of 840 MHz (3.00-3.84 GHz) and 310 MHz (5.94-6.25 GHz), which resonates at dual bands, viz., 3.42 GHz and 6.07 GHz. The impedance bandwidth (S₁₁<-10 dB) is 25% for the first band and 5.1% for the second band. The size of the antenna is 31 × 25 × 1.6 mm³ realized on a low-cost FR-4 Epoxy substrate. This antenna can be effectively utilized in worldwide interoperability for microwave access (WiMAX) and wireless access in vehicular environments (WAVE) applications. The prototype of the proposed antenna is fabricated and measured. Simulated and measured results are in agreeing nature. Experimental and simulated analyses of the antenna including parametric and dispersion characteristics are dealt in this communication.

Linear antenna array design is a multi-parameter, multi-objective, and nonlinear problem which requires optimal design parameters to get desired performance. To achieve desired performance through multi-objective optimization process, a compromise among desired objectives is essential. In such a situation to make a rational decision on global optimization to avoid arbitrary compromise to any objective, we introduced two fuzzy logic biased/fuzzy biased optimization techniques. We proposed fuzzy logic biased biogeography based optimization algorithm and fuzzy biased gravitational search optimization algorithm to solve M-element nonlinear linear antenna array design problem. In our design problem, we have considered a 16-element dipole-linear antenna array. The optimal design problem incudes thirty one design parameters (sixteen lengths, and fifteen spacings) and four performance parameters such as directivity, front to maximum side-lobe level, half power beamwidth, and front to back ratio. The result shows that applications of fuzzy biased optimizations are more efficient for solving multi objective problem. While analysing the linear antenna array, mutual coupling is taken into account for numerical analysis using method of moment.

In this paper, a broadband planar modified quasi-Yagi antenna using a two-element log-periodic dipole array as a driven element is proposed. To feed the two-element log-periodic dipole array, a simple microstrip to stripline transition as a balun is designed, which converts the unbalanced input to balanced output. The antenna is fabricated on a low cost glass epoxy FR4 substrate with dielectric constant = 4.4, substrate thickness = 1.6 mm, and loss tangent = 0.02. The overall size of the antenna is 84 mm×111 mm, which is 0.41λ_o×0.54λ_o at the center frequency of 1.45 GHz. Measured results show a bandwidth of 41.4% for VSWR≤2. A gain of 6.5 dBi±0.5 dB and front to back ratio (F/B) of better than 20 dB are achieved over the bandwidth. Measured results are in good agreement with the simulated ones. This antenna is useful for RFID, portable direction finding, spectrum monitoring systems, etc.

The bandwidth of OAM antennas, which have a great potential for multiple-input multiple-output (MIMO) communication, must be wide enough. Unfortunately, most of researchers only care about the generation and characteristics of vortex beams carrying orbital angular momentum (OAM) but ignore the bandwidth of OAM antennas. To develop OAM antenna suitable for MIMO communication, Vivaldi antenna is used as the element of circular array because of its wide bandwidth. Three compact wideband circular Vivaldi antenna arrays that can generate vortex beams carrying OAM with numbers of modes l=0, -2, +2 are proposed and experimentally validated in this paper. Measured results show that the proposed antennas can radiate vortex beams with different numbers of modes over a frequency range of 2.7-2.9 GHz.

A novel W-band WR 10 waveguide to microstrip line transition is designed, simulated in a 3D full-wave EM simulation software, fabricated, and evaluated by measurements. The main advantages of this transition are frequency-flat transmission, low reflection, and uncomplicated fabrication. Simulation shows a reflection coefficient of better than -23 dB from 75 to 90 GHz for one hollow waveguide to microstrip line transition. The port reflections increase for a fabricted prototype with two transitions and a connecting microstrip line to a level of about -14 dB. This is mainly caused by fabrication tolerances. The overall transmission of the dual transition prototype is found at a very satisfactory level of about -4.8 dB at 90 GHz for a connecting microstrip line with a length of 45 mm corresponding to an estimated loss of approximately 0.6 dB for a single transition.

In this paper, measurement, modeling and validation of existing models on the effect of nonhomogeneous vegetation on UHF radio-wave propagation through a long forested channel at frequency of 1835 MHz are reported. The paper focuses on vegetation attenuation measurement through a long forested channel of about 8 km long with mixed vegetation of different density. The measured data were fitted using exponential decay function, and a new model was proposed from the fitted curve. The new proposed model will take care of the limitation in vegetation depth posted by some existing models. Generic models, mainly modified exponential decay and analytical models were also fitted to the data and validated, while RMSE was used to determine the best model that describes the data. The evaluated data results show that all the models tested give significant errors which show that they are not suitable for long forested channel scenario. Though COST 235 has the least error (17.05 dB), the error is still significant because COST 235 could only account for vegetation attenuation of short distance scenario. Attenuation shows corresponding increase with increase in leaves thickness in the forested channel considered, which was due to complex permittivity of the leaves moisture content and the dielectric properties of the leaves saline water. The developed model and other results obtained in this study will help to improve prediction accuracy of the effects of vegetation attenuation in nonhomogeneous vegetation along forested channels and also help in establishing efficient UHF radio link budget for long forested channel scenario.

A new type of three-dimensional (3D) Frequency Selective Surfaces (FSS) applied to passive sensing in Structural Health Monitoring (SHM) is presented. Such passive FSS sensors are proposed as an alternative to conventional sensors to eliminate the need of DC/AC power. Moreover, these FSSs are modified in a 3D form to feature enhanced performance compared to conventional FSSs and sensors. More specifically, the proposed 3D FSS is able to control its sensitivity |S₂₁| in either TE or TM incident waves. In this project, incident angle characteristics are evaluated for SHM applications to obtain angular responses of up to 80 degrees. The resonant behavior of the TE-incident wave is shown to be sensitive towards the incident angle and is suitable to be used for monitoring any building tilting and damage. This is due to the significant 3D length changes of the conductor elements. Meanwhile, the TM-incident wave is found to be insensitive towards the incident angle.

novel Ultra-wideband Willis-Sinha Tapered Slot antenna for landmine detection using Ground Penetrating Radar (GPR) system with enhanced gain and directivity is presented. The structure is constructed on a 235x270 mm² FR4 dielectric substrate. The antenna is fed by a novel tapered coplanar waveguide (CPW) to coplanar stripline (CPS) transition feed. The antenna's impedance bandwidth is extended by adding an antenna arm constructing parabola shape with the antenna element. The antenna has a corrugated structure along the antenna outer edges to improve radiation efficiency and get higher directivity. Also, a mushroom-like circular EBG structure is used in the lower side of the antenna arm to reduce interference and enhance front-to-back ratio (F/B ratio). A partial substrate removal, like circular cylinders inside the substrate, is aligned with the antenna tapered profile to obtain better radiation efficiency and enhance antenna gain. The operational bandwidth of this antenna extends from 0.18 to 6.2 GHz. The minimum return loss reaches 60 dB. The average directivity reaches 12.2 dBi while the gain and radiation efficiency are 11.8 dBi and 92%, respectively with gain enhancement of 195% due to using corrugated structure and air cavities. The front-to-back ratio (F/B ratio) is 23 dB. Also, a size reduction of 48% is achieved due to using extended arm. The antenna performance was simulated and measured. Good agreement was found between numerical and experimental results. The proposed antenna is suitable for various ultra-wideband applications especially in landmine detection. The design of the proposed antenna is given in very simple five design steps.

A novel compact wideband printed loop antenna is presented for wireless applications. The wideband characteristic is achieved by combining three dierent loop resonant modes of the antenna. The antenna geometry is simple and consists of a rectangular meandering loop, a coplanar waveguide (CPW) structure, and a monopole feed. This proposed antenna has a dimension of only 27×20×1 mm³ while operates at a wideband from 2.4 GHz to 5.9 GHz (84.3%) with stable gain, radiation pattern and vertical linear polarization. This antenna is suitable for WLAN and future 5G sub-6 GHz spectrum communications. Good agreement between the simulation and measurement is obtained.

This paper studies the impact of current harmonics on the synchronous reluctance machine's average torque and torque ripple. The electromagnetic model of a general m-phase synchronous reluctance machine which integrates the inductance and current harmonics is developed. This model shows that there exist two mechanisms that generate an average torque with a non-zero average value: the proper contribution of the current harmonics and the interaction between them. This model is then used in the case of a 2-phase synchronous reluctance machine with a common transversally laminated anisotropic rotor. This machine design shows negligible inductance harmonics with respect to its fundamental value. Therefore, it has been found that the interaction between the 3rd and 5th current harmonics generates a torque equivalent to the torque generated by the fundamental current component. A locus of the current harmonic components that deliver a constant torque is determined. Furthermore, we have found that, on this locus, the machine torque ripple decreases significantly. Experimental data validate the developed theoretical work and show that at the same torque, the torque ripple is reduced from 20% to 4%.

New zeroth-order resonators (ZORs) are utilized as parasitic elements to enhance a microstrip antenna's bandwidth. By utilizing mushroom T/L shaped resonators, extra resonances are generated. Then, by merging the resonances of the microstrip antenna and the T/L shaped resonators, a wideband antenna is obtained to cover the 5.15-5.35 GHz wireless local area network (WLAN) band. As the ZORs are embedded in the patch of the microstrip antenna, the usages of the parasitic elements do not increase the antenna size. Moreover, as one ZOR resonance is lower than the microstrip patch resonance, a compact antenna is realized. The patch size is decreased from 0.27λ_c×0.42λ_c×0.027λ_c of the reference microstrip antenna (RMA) to 0.25λ_c×0.40λ_c×0.026λ_c of the proposed ZOR based microstrip antenna, where λ_c is the wavelength of their corresponding lower cutoff frequencies. The proposed antenna was fabricated and measured. The simulated and measured -10 dB impedance bands of the proposed antenna are 5.06-5.40 GHz and 5.07-5.42 GHz, respectively. And, its bandwidth increases 70% compared to the RMA. The simulated and measured patterns are stable in the whole operating band. The gains of 4.73 dBi and 4.24 dBi are measured at the ZOR modes, and 7.88 dBi is measured at the microstrip patch mode.

Vehicle-to-Vehicle (V2V) communications are characterized by dynamic environments due to the movement of the transceiver and scatterers. This characteristic makes V2V channel modeling particularly challenging. In this paper, a three-dimensional (3-D) geometrical propagation model and a generalized 3-D reference model that include line-of-sight (LoS) and single bounced (SB) rays are proposed for multiple-input-multiple-output (MIMO) V2V multipath fading in different roadway scenarios (e.g., flat roads, intersections and arcuate overpasses). In the models, the transceiver can move with nonlinearly varying velocities in nonlinearly varying directions, and each scatterer can move with a random velocity in a random direction. The corresponding space-time correlation functions (ST-CFs) are analytically investigated and numerically simulated in different roadway scenarios. Finally, the modeled Doppler power spectral density (D-PSD) is compared with the available measured data. The close agreements between the modeled and measured D-PSD curves confirm the utility of the proposed model.

A novel method is proposed and demonstrated to generate ultrahigh speed, ultrashort flat-top picosecond electrical pulses by combining laser pulse shaping with ultrafast electro-optics sampling technique. Starting with high repetition rate laser pulses, a sequence of birefringent crystals is employed to produce optical pulses with flat-top temporal profile and tunable duration. Subsequent measurement of optical waveforms by an ultrafast photodetector yields high-speed, ultrashort flat-top picosecond electrical pulses. By using two sets of YVO4 crystals for laser pulse shaping, we report on the generation of 704 MHz, 48 picoseconds and 704 MHz, 88 picoseconds flat-top electrical pulses with 16-30 picoseconds rise or fall time. To the best of our knowledge, these results are better than or comparable with the best performance using step recovery diodes and the direct electro-optics sampling technique.

A simple single feed circularly polarized microstrip antenna with Koch curve as boundary is presented. The two pairs of rectangular microstrip antenna edges are replaced by a Koch curve of 1st stage and 2nd stage with different indentation angles to get circular polarization. The proposed method is simple and easy to obtain circular polarization with reasonable 3 dB axial ratio bandwidth and 10 dB impedance bandwidth. The dependency of aspect ratio and fractal dimension of the boundary on the performance of the circularly polarized antenna is discussed.

We investigate the diffraction modeling of a plane wave by an infinitely thin and deformed perfectly conducting strip. We show that the diffraction pattern in the Fraunhofer domain can be obtained from efficiencies calculated for a periodic surface with an interpolation relationship; the elementary pattern of the periodic surface is identical to the strip. We consider the case where the deformation amplitude of the strip is small compared to its width. In this case, the propagation equation written in a curvilinear coordinate system is solved by a perturbation method inspired from quantum physics and extended to imaginary eigenvalues for evanescent waves. In the Fraunhofer approximation domain where the only waves are the propagative waves, the diffraction pattern obtained for a sinusoidal profile strip shows the phenomenon well known as apodization. Classically this phenomenon is obtained for physical optics with a slot in a screen with a variable transparency function similar to the profile function of the strip.

This paper presents low cross-polarization single-layer reflectarray elements for dualpolarization use. These elements have an omega-shaped symmetrical structure to realize the crosspolarization reduction and also provide parallel linear reflection-phase properties with almost the same slop characteristics for the frequency, thereby achieving the desirable reflection phase range more than 360˚ over the wide frequency range. To verify effectiveness of the proposed elements, a reflectarray antenna with an offset feed is constructed by them, and wideband frequency characteristics are also confirmed at Ku-band numerically and experimentally.

In this paper, a three layer composite chiral metamaterial (CCMM) is proposed to achieve diode-like asymmetric transmission and high-efficiency cross-polarization conversion by 90° polarization rotation with ultrabroadband range simultaneously in microwave region, which was verified by simulation and experiment. This CCMM is composed of a disk-split-ring (DSR) structure sandwiched between two twisted sub-wavelength metal grating structures. The simulation agrees well with experiment in principle. The simulation results indicate that the incident y(x)-polarized wave propagation along the -z (+z) direction through the CCMM slab is still linearly polarized wave with high purity, but the polarization direction is rotated by ± 90°, and the polarization conversion ratio (PCR) is greater than 90% in the frequency range of 4.36-14.91 GHz. In addition, in the above frequency range, the asymmetric transmission coefficient (Δ_lin) and the total transmittance (T_x) for x-polarized wave propagation along the -z axis direction are both over 0.8. Finally, the above experiment and simulation results were further verified by the electric field distribution characteristics of the CCMM unit-cell structure. Our design will provide an important reference for the practical applications of the CCMM for polarization manipulation.