فهرست مطالب kambiz afrooz

Electromagnetic susceptibility (EMS) of a power amplifier (PA) against an interfering wave is presented. The interfering waves affect the performance of any circuit, either intentionally or from adjacent equipment. In the case of power amplifiers, this phenomenon can overdrive the PAs into the nonlinear region and if the interfering wave still exists, it can damage the PA. Therefore, circuit designers must design the circuit to be not susceptible to interfering waves, as much as possible. In this article, EMS analysis of a PA against an interfering Gaussian modulated pulse with the 3D finite difference time domain (3D-FDTD) method is presented. In this method, the transistor is replaced with an appropriate transistor nonlinear large-signal EEHEMT circuit model, and the whole circuit of the PA including the transistor circuit model, matching networks, and biasing circuits is simultaneously analyzed in the presence of radiated and conducted interferences. This method gives more accurate results than the hybrid methods that analyze the active and passive parts of the amplifier separately. This method is applied to a designed PA with Wolfspeed’s CGHV1J006D discrete GaN on SiC high electron mobility transistor (HEMT) and a hybrid method is proposed to validate the results. The results show a good agreement between the proposed and the validation method.

In copper electrodeposition methods, by applying an electric current between two electrodes immersed in an electrolyte containing CuSO4- H2SO4-H2O, copper is deposited on the cathode surface. Presence of magnetic field has a considerable effect on the performance of electrodeposition cells. The most important roles of the magnetic field on these processes are Lorentz force, magnetohydrodynamic (MHD) convection and its interaction with the natural convection induced by the concentration gradient. In this study, an unsteady, two-dimensional copper electrolysis (one phase) and electrowinning (two-phase liquid-gas) cells were simulated in the presence of magnetic field by using Computational Fluid Dynamics (CFD). The equations of Nernst-Planck, momentum and electric potential were solved by finite volume method. The Eulerian-Lagrangian method was used in simulation of two-phase copper electrowinning cell. The simulation results of electrolysis process showed a good agreement in comparison with experimental data of Muhlenhoff et al. After the validation of the model, copper concentration change and velocity profiles of two processes were investigated and compared with each other. The simulation results showed that the MHD interaction with the natural convection and also intrusion layer pile up leads to the velocity decay. As a result, the velocity reduction in the electrowinning process occurs later than in the electrolysis process but its reduction in the second stage of electrowinning process is about 93%, which is much more than 33% in the electrolysis process.

A power divider (PD)/ power combiner (PC) with high quality factor and enhanced output ports isolation using substrate integrated waveguide (SIW) technology is proposed. An SIW cavity is designed to provide a high quality factor filtering response and an SMD resistor is attached between two output ports to realize the high isolation. The value of the applied resistor is calculated by using the even and odd mode analysis. The measured results obtained from testable model are in a good agreement with the simulated results. These results show that the return loss is 23 dB, the minimum insertion loss is 4.55 dB including intrinsic 3 dB insertion loss of PD, and the isolation between output ports is 20 dB, which seems the proposed design could be an important component in microwave circuits.

A compact and sharp-rejection ultra-wideband (UWB) microstrip band-pass filter (BPF) is developed using of left handed metamaterials realized by complementary split ring resonator (CSRR). Moreover, proposed structure consists of two doublets parallel coupling gaps at each side of a microstrip ring. In comparison with some other filters, this structure shows a significantly wider passband due to the introduction of a cross-coupling between the feed lines (input and output) which generate four pairs of attenuation poles in the passband.On top of that, using two CSRRs etched in the back substrate side,and series gap inside the microstrip ring leads to the addition of two extra transmission poles at the lower and upper edges of the filter.Consequently, a compact six-pole ultra-wide bandpass filter is designed which exhibits extremely sharp rejection skirts around the target passband.
The proposed filter has a passband covers3.4 to 10.15GHz andits measured 3dB fractional bandwidth is about 100%. Furthermore, rejection level better than 20 dB in upper stopband is extended to around 15.2 GHz both in simulation and measurement. Experimental verification is provided and good agreement has been found between simulation and measurement. To our knowledge, the size of proposed ultra-wideband filter is more compact in comparison with known similar filters.

In this pare, a wideband three-order bandpass filter (BPF) is proposed. The proposed wideband filter is designed using the substrate integrated waveguide (SIW) structure by loading T-shape slots. A BPF with two resonators is formed by etching T-shape slots with different size on the top metal plane of the SIW structure. The filter is investigated with the theory of coupled resonator circuits. The T-shape slots, etched on the SIW structure, are used to form up a new multiple-mode resonator (MMR) in order to achieve a wide passband of operation while keeping the overall size of the proposed filter to be much compact. The design procedure as well as design curves of the filter are given and discussed here. Compared with some other reported BPFs with SIW technique, the presented BPF using the SIW structure loaded by T-shape slot has great improvements on size reduction and selectivity. In order to prove the validity, the proposed wideband SIW BPF on a single layer printed circuit board (PCB) is designed and experimentally examined. The measured results show that the filter achieves an insertion loss of 1.1 dB at 6.4 GHz and a return loss of higher than 21 dB. The proposed filter has a pass-band covers 5.1 to 7.99 GHz and its simulated and measured 3 dB fractional bandwidth is about 44.3%. The measured results are in a good agreement with the simulated results.

A four-way power divider/power combiner using substrate integrated waveguide (SIW) and microstrip lines is proposed and investigated. The proposed power divider consists of a double-layer substrate with a bottom layer including an SIW T-junction and a top layer including a microstrip network. This microstrip network consists of a modified Gysel power divider which provides a high isolation between output ports by using two grounded resistors. Meanwhile, this modified Gysel power divider maintains high power-handling advantage over Wilkinson power divider. A transition between the SIW T-junction and microstrip network is realized by etching two rectangular slots on the middle metal layer. The even-odd mode method is used to analyze the presented structure. A prototype of the proposed power divider is designed, simulated, and fabricated. The results show that the return loss of the input port is better than 12 dB over 8.43 to 10.57GHz. Also, the output return losses and isolation are better than 10.5 dB over the whole bandwidth.

This paper presents a filtering power divider (PD)/power combiner (PC) using substrate integrated waveguide (SIW)-based 180o hybrid. The utilized 180o hybrid includes a standard H-plane 3-dB coupler and a broadband 90o phase shifter. The phase shifter is composed of non-radiating longitudinal slots patterned on the top conducting surface of the SIW. We have added the filtering property to the structure by an array of dissimilar transverse slots. The slots dimensions are obtained by the extracted external quality factor, coupling coefficient and the relationship between them and the slots dimensions. The proposed structure is designed for 8.2 GHz and investigated by ADS simulator. The results show the fractional bandwidth of the sum and difference ports are 13.7% and 14.93%, respectively. For sum operation, the minimum insertion loss is 3.78 dB and the return loss is above 25 dB in the passband. For difference operation, the minimum insertion loss is 3.81 dB and the return loss is above 26 dB in the passband.

In this paper, a fully distributed model for a single pole single throw traveling wave switch is introduced and important parameters of the switch such as insertion loss, isolation, and reflection coefficient are presented based on the lossy transmission line model of switch. The results of fully distributed model are compared with the semi-distributed model’s results and have good agreement with them. By applying the fully distributed model and calculating various switch’s parameters as a function of the switch length and operating frequency, the optimum switch length and operating frequency are obtained versus the parameters of switch, especially the reflection coefficient and isolation in OFF and ON conditions.