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.

This article basically deals with the implementation of a negligible resistance varactor with a wide capacitance value into a modified version of a cedar shape antenna [1]. The electromagnetic characteristics of the antenna are manipulated both at the level of fractal geometry and electrical length using diodes. The antenna achieves tunability in a wide frequency range as a quad band antenna operating between 1.45 GHz and 4.6 GHz when 3 pairs of varactors are connected across slots. Pin diodes are also implemented leading to tunability in triple frequency bands between 3.7 GHz and 5.8 GHz. Moreover, implementing pin diodes as switches allows frequency reconfigurability of a dual band between 2.5 and 4 GHz and a single band of 6.6 GHz. The antenna RF frequencies have many applications in wireless communication that cover GPS, Bluetooth, WIFI, WIMAX and WLAN.

Dielectric or magnetic materials introduced in a wireless power transfer (WPT) system affect the properties of WPT. This paper quantitatively studies the coupling between the transmitting and receiving elements for a WPT system including either dielectric or magnetic materials. The transmitting and receiving elements are open spirals and solenoid coils which are usually used in WPT systems. The analysis method is the perturbation method which can calculate the total coupling coefficient k, the electric coupling component k_e and the magnetic coupling component k_m simultaneously. This paper gives quantitatively analyzed data on k_m and k_e to indicate how much k_m and k_e are affected by a dielectric or magnetic material introduced in a WPT system.

The well-known ``Sommerfeld radiation problem" of a small -Hertzian- vertical dipole above flat lossy ground is reconsidered. The problem is examined in the spectral domain, through which it is proved to yield relatively simple integral expressions for the received Electromagnetic (EM) field. Then, using the Saddle Point method, novel analytical expressions for the scattered EM field are obtained, including sliding observation angles. As a result, a closed form solution for the subject matter is provided. Also, the necessary conditions for the emergence of the so-called Surface Wave are discussed as well. A complete mathematical formulation is presented, with detailed derivations where necessary.

The Meissner effect is explored based on the acceleration-dependent component of the Weber force. According to the Maxwell theory, a steady circulating current does not produce any dynamics on external resting charges; however, according to the Weber theory, the charges of the circulating current exhibit a centripetal acceleration, which affects the external charges at rest. It is demonstrated that the current generated in this manner can explain the Meissner effect in classical physics.

This paper considers an ideal planar transformer wherein only the electromagnetic parasitics (stray capacitive and leakage inductance) arising out of the transformer geometry are taken into account, assuming lossless conditions. A suitable electrically equivalent circuit model for the planar transformer is used to analyze its frequency and power transfer characteristics; this model was validated by a three dimensional electromagnetic simulation of the planar transformer structure in FEKO electromagnetic simulation software. The effect of dielectric thickness on the bandwidth of the transformer has been analyzed based on the premise that the inherent stray capacitance and leakage inductance elements would affect the power transfer characteristics of the transformer. It has been found that the dielectric thickness of a planar transformer can be optimized so as to maximize the frequency bandwidth. It is also shown that the bandwidth is found to be sensitive to the thickness of the dielectric beyond the optimum thickness threshold topt. Convenient closed form analytic expressions for the optimum dielectric thickness and the resultant maximum bandwidth are derived and presented. It is argued that these results can be readily used to benefit the design of air-core PCB/Planar transformers.

A compact ultra-wideband (UWB) antenna with simple structure is presented. To achieve UWB performance with a compact size, two open ended rounded inverted L-shaped slots are etched on the square ground plane. Moreover, further bandwidth enhancement is obtained by cutting a bevel on the asymmetrical radiating patch. The antenna is fed by a 50 Ω microstrip line and has a small size of 28 × 28 × 1.6 mm³. The simulation time- and frequency-domain results obtained from HFSS simulator package are verified by experimental measurements. Both simulated and measured results show that the antenna can provide a wide impedance bandwidth of more than 129% from 2.7 to 12.55 GHz with -10-dB reflection coefficient. Besides, it is shown that by introducing several antenna designs, the impedance bandwidth can be enhanced from 58% to 129%. The effects of the key design parameters on the antenna impedance bandwidth are also investigated and discussed. Measured results for the reflection coefficient, far-field radiation patterns, radiation efficiency, gain, and group delay of the designed antenna over the UWB spectrum are presented and discussed. Measured data show good concordance with the numerical results. Also, the fidelity factor is calculated in both E- and H-plane by using CST Microwave Studio. The obtained results in both time- and frequency-domain indicate that the antenna is a good option for UWB applications.

А rigorous approach to study the fast H-waves which propagate across an infinite double comb array (IDCA) is proposed. It is based on the Floquet theorem combined with the advanced moment method (Galerkin) scheme in which the basis explicitly satisfies the edge conditions at the rectangular wedge. An exhaustive analysis of the regular and singular modes of the IDCA is made. Normalized critical wave numbers and modal fields are investigated in terms of geometrical parameters. Coupling effects between different IDCA modes are found. For the singular modes a new analytical formula for the critical normalized wave numbers is obtained.

Conformability helps microstrip antenna to mount on any geometry platform and can also be used for multiple frequency systems without any complexity. The designing of a frequency reconfigurable antenna conformal to cylindrical surface using the combination of metamaterial (MTM) and substrate integrated waveguide (SIW) is proposed. The single and dual antenna models resonate at various frequencies of C-band by means of changing the cylindrical curvature. The results also show a considerable improvement in bandwidth and gain for dual antennas as compared to the single antenna. The antenna parameters are simulated on HFSS tool, and validation process is done by experimental setup.

Thomson scattering of an electromagnetic wave in a plasma density irregularity is considered. A new effect is found that the scattered waves generation and superposition near the electron density extremum may result in a substantial modulation of the scattered signal frequency spectrum. Due to this effect, the observable spectrum shape will be substantially different from that for the electron density fluctuations. This fact should be taken into account when interpreting Thomson scattering experiments.

A broadband ultra-high frequency reader antenna based on magnetic coupling is proposed for radio frequency identification (RFID) near-field applications. The design utilizes four quarter-wave impedance transformer double-side parallel stripline (QDSPSL)-fed dipoles to form a square region to achieve broadband impedance matching and strong and uniform magnetic field distribution. The phases of currents on each dipole are kept same, thus, strong distribution of magnetic can be generated by the antenna. A 200 × 200 × 1.6 mm³ antenna has been fabricated on an FR-4 substrate to fit RFID near-field application. The measured 10-dB impedance bandwidth is 107 MHz (860-967 MHz), which covers the entire UHF RFID frequency band (860-960 MHz). Measured tests on the antenna read range are carried out by observing the feedback received signal strength indication (RSSI) values, exhibiting a large reading region of 140 × 140 mm² and 100% reading rate within 100 mm for near-field tags.