نشریه الکترومغناطیس کاربردی
سال ششم شماره 2 (پیاپی 17، پاییز و زمستان 1397)

This paper highlights the future perspective for novel hybrid radial-axial flux structure magnetic gear, named arcuate double-sided magnetic gear (ADSMG) with the aim of higher torque density transmission. Its performance characteristics are quantitatively analyzed using an improved quasi 3-D analytical method (IQAM) computations of magnetic field (which is an improved and amended of 2-D analytical method). Results are verified by 3-D finite-element method simulations to enhance the reliability and precision of the analysis. This modeling is carried out by an effective dependent modeling for the different components of magnetic field distribution, based on axial and radial flux magnetic gear topologies, and modified to accurately model the proposed ADSMG structure. Utilization of proposed IQAM for optimization of ADSMG in a typical wind power application is investigated. It is shown that the optimized ADSMG has significant and superior advantages in terms of torque density than the traditional MGs.

A conformal array with directive patch antenna element is designed and proposed to achieve optimum direction of arrival performance. The MUSIC method is used for the proposed array evaluation and compassion where the antenna radiation patterns extracted from the full wave simulation software are encountered in the DOA estimation process. Antenna mutual coupling and radome effect are among the radiation patterns used to achieve more precise results. The simulations results prove that conformal array achieves better DOA estimation performance than the planar array antenna especially in the horizontal plane. Moreover, the conformal antenna array angle is evaluated to achieve optimum conformal array structure.

This paper presents a merged low noise amplifier (LNA) and mixer for wireless local area networks (WLANs) applications. The proposed down-conversion LNA-mixer is designed for 2-3 GHz radio frequency (RF) band and an intermediate frequency (IF) of 100 MHz using RF-TSMC CMOS 0.18 μm technology. A new input matching network is introduced for common source LNA to provide good input matching. In addition, the conversion gain (CG) and noise performance of the LNA-mixer are improved by employing an active load and current bleeding technique in the mixer. The proposed LNA-Mixer has been simulated by Advanced Design System (ADS). Simulation results show the high conversion gain of 15–17 dB and low double side-band noise figure (DSB-NF) of 4±0.5 dB as well as high isolation between ports at frequency band of 2-3 GHz. Monte Carlo simulations has been done for the proposed LNA-mixer with 100 samples to verify the impact of process variations and mismatch. For the conversion gain and for DSB-NF, simulation results show respectively a mean (μ) of 15.7 dB with standard deviation (σ) of 0.11 dB, and μ=7.4 dB with σ=0.37 dB and confirm their low sensitivity to process variations. The proposed LNA-Mixer operates at the supply voltage of 1.5 V with power consumption of 19.8 mW.

Finite difference and finite element methods have more accuracy in the calculation of photonic crystal fiber (PCF) characters than other methods. In the present paper the finite difference method in the frequency domain is used to describe and determine the characteristics of PCF. The propagation characteristics of photonic crystal fiber with eight-hole layer are calculated and the fiber characteristics, consisting of, effective refractive index and waveguide dispersion are determined. Then using the composite Simpson rule for double integral, the values of effective areas and numerical apertures are obtained using the results of fields for different values of the hole sizes and distances and the results are compared. Since the determination of zero dispersion region is important in telecommunication and especially for the design of compensators, by determining the color dispersion and zero dispersion wavelength in this kind of fibers, the effects of air hole characteristics in the zero point of dispersion is verified. In this paper for the first time, using the mentioned method, the effects of the hole size in PCF characteristics such as waveguide dispersion is calculated and it is shown that increasing the air hole size in the fixed hole distance, causes the zero dispersion wavelength to decrease and for the fixed air hole with increasing the hole distance, the zero dispersion wavelength increases in the PCF..

In this paper, the design theory of an 8 GHz oscillator based on a new structure of active dielectric resonators is presented. The new structure emphasizes on phase noise reduction by employing only one active device. The proposed structure uses additional feedback from transistor to resonator in order to increase the quality factor. Measurement results report that phase noise is reduced to -145.19 dBc/Hz at 100 kHz offset frequency which represents 12 dB improvement compared to oscillators with passive dielectric resonators. Also, compared to oscillators with conventional active resonators, noise source of the second amplifier which makes spurious oscillation is removed. The size and power consumption are reduced since one transistor is used in the presented structure. This structure performs the lowest phase noise compared to oscillators with other dielectric resonators.

In this paper, using a two-dimensional photonic crystal, a compact and simple structure is introduced for an all-optical AND logic gate. The designed structure consists of three photonic crystal waveguides connected by a nano resonator. The nano resonator is formed by increasing the radius of the dielectric rod. Analysis and investigations have been done using the finite-difference time-domain and plane wave expansion methods. The plane wave expansion method is used to obtain photonic band gap and finite-difference time-domain method is used to study the electromagnetic field behavior in photonic crystal structure. The advantages of this design are small dimension, the high possibility of realization, and high output power in logical state of 1. The delay time of this gate is 0.32 ps. The minimum ratio of the received optical power to the input power in logical state 1, is 1.968 and the maximum ratio of the optical power to the input power in logic zero mode is 0.492. So, the contrast ratio for the designed logic gate is 6 dB. The high output power allow the logic gate to enable to be integrated the next level logic gates into the optical integrated circuits. Considering the features mentioned, this logic gate can be used in optical integrated circuits.