Journal of Communication Engineering
Volume:3 Issue: 1, Spring 2014

In this paper, analysis, simulation and design of a distributed amplifier (DA) with 0.13µm CMOS technology in the frequency range of 3-40 GHz is presented. Gain cell is a current reused circuit which is optimum in gain, noise figure, bandwidth and also power dissipation. To improve the noise performance in the frequency range of interest, a T-matching low pass filter LC network which is utilized at the input gate of the designed amplifier. By this means, the proposed cascaded DA shows about % 28 improvements in noise figure and 20% improvement in the gain compared with those of the other well-known configuration. To show the capability of the proposed method we also compared the figure of merit of the proposed amplifier with those obtained with the other researches and showed that this figure is around 38% higher than that of those achieved by other researchers. The figure of merit includes gain, bandwidth, power consumption and also noise figure.

The design, simulation, fabrication, and measurement of two structures of metamaterial absorbers (MA) is investigated at microwave frequency in this paper. By stacking of one layer structure on the top of each other, a two-layered structure is generated. The unit cell at each layer consisting of two sets of various circular and square patches are designed so that the structure exhibit quad band absorption response. The advantages of these MAs are being thin, having simple structures, excellent polarization characteristics and maintaining high absorption peaks even at large angles of incidence for both TM and TE polarizations. In addition, measurement of a fabricated prototype shows a satisfactory agreement with the respective simulation results.

An equivalent circuit model for predicting the frequency response of a square ring slot frequency selective surface (SRS-FSS) for normal incidence is described. The proposed FSS consists of an array of square patches centered within a wire grid. The presented circuit model is formed by the impedance of the wire grid that is parallel with the impedance of the patch array, also the mutual coupling between the wire grid and the patch array is taken into account in the patch impedance. Through using the provided relations, the values of circuit elements can be calculated. The proposed relations are applied to many SRS-FSSs with different dimensions and the results are compared to those of the simulations obtained from two well-known software packages, Ansoft HFSS and CST Microwave Studio. The results show that the proposed model well approximates the frequency behavior of the SRS-FSS.

In this research work, a multibeam antenna which is a combination of a beamformer network (BFN) and a linear array antenna, has been designed. A Rotman lens has been chosen as beamformer network and Vivaldi antennas have been selected for constructing array antenna. The Substrate Integrated Waveguide (SIW) was used for implementing Rotman lens. After explanation the structure of Substrate integrated waveguide, a prototype SIW Rotman lens was designed to create 7 beams at angles of 0°, ±10°, ±20° and ±30°. Each beam is corresponding to one of the input port of Rotman lens. This Rotman lens was designed for aeronautical applications and operates at center frequency of 16 GHz and frequency bandwidth of 1 GHz. It was found that the amplitude and phase distributions at output ports of Rotman lens are appropriate. Then a linear array of 7 Vivaldi antennas was connected to the Rotman lens to realize the multibeam Rotman lens antenna.

In this paper, genetic algorithm-based approach for transient analysis of single transmission line connected to arrester is proposed. In this approach, the lightning channel striking the overhead line is first represented by a current source and this source is truncated by a finite set of frequency harmonies in time domain. Norton equivalent circuit viewed across arrester is then computed by method of Fuzzy (MoF), then applying Kirchhoff’s current low to this nonlinear circuit and solving it by genetic algorithm, transient voltage across the arrester is easily computed. Comparison of the achieved voltage with accurate one (EMTP software) shows good agreement as well as fast run-time.

Distributed storage systems are mainly justified due to their ability to store data reliably over some unreliable nodes such that the system can have long term durability. Recently, regenerating codes are proposed to make a balance between the repair bandwidth and the storage capacity per node. This is achieved through using the notion of network coding approach. In this paper, a new variation of these codes, called hybrid regenerating codes incorporating a super node is proposed, showing in some cases the new code outperforming existing regenerating codes in terms of the repair bandwidth and/or download cost.