فهرست مطالب

Majlesi Journal of Telecommunication Devices
Volume:4 Issue: 2, Jun 2015

  • تاریخ انتشار: 1394/04/03
  • تعداد عناوین: 6
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  • Zahra Habibi, Morteza Kazerooni, S.Hossein Mohseni Armaki Pages 37-41
    Phase shifters are devices, in which the phase of an electromagnetic wave of a given frequency can be shifted when propagating through a transmission line. In many fields of electronics, it is often necessary to change the phase of signals. RF and microwave phase shifters have many applications in various equipments such as phase discriminators, beam forming networks, power dividers, linearization of power amplifiers, and phase array antennas. Phase shifters are divided into two group diode and ferrite. In this paper a ferrite phase shifter is investigated. Ferrite phase shifters are two-port devices that may be either analog or digital with either reciprocal or nonreciprocal characteristics. In previous works, magnetic flux densityB-magnetic field intensity curve or B-H Hcurve of a ferrite core is obtained. In this paper, phase shift-current curve or Ø-I curve of a reciprocal analog ferrite phase shifter is simulated and the effect of various parameters tolerances, such as permeability, permittivity, frequency and length of ferrite rod on the Ø-I curve is shown.
  • Samaneh Matindoost, Majid Baghaei-Nejad, Ghasem Sadeghi Bajestani Pages 43-49
    In this paper, we proposed a low noise amplifier (LNA) for ultra wideband (UWB) applications using TSMC 0.18µm CMOS technology. LNA and high frequency H-shaped antenna have been utilized to solve problems of each block, such as the necessity of being matched with 50 Ohm impedance, so we have one more degree of freedom and a more complex system, although our choosing ability is increased.The targeted is Ultra Wide Band where this architecture and a Co-Designed version, with UWB-LNA architecture offer one of the best compromises between gain and noise figure.For having the best trade-offs between these two cases in UWB-LNA, both Multi-Objective Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) are used successfully. Symmetric nature is obtained both in terms of S-parameter as well as flatness over a wide bandwidth for gain and noise figure.To have better Co-Design; in this work another optimization on antenna parameters performed with ADS Software.In co-optimization with the aid of two techniques; LNA parameters improvement utilizing evolutionary algorithms and antenna parameters enhancement in co-design output S-parameters had more promising results.Results show gain-flatness is being enhanced in desired frequency band. Noise factor is improved by more1.5 dB over the whole bandwidth [3.1GHz-8.1GHz]and supply voltage of 1.8V.
  • Mohammadreza Pashaei, Amir Rastegarnia Pages 51-56
    In this research crosstalk phenomenon in DWDM two-channel communication demultiplexer was reduced by optimizing 2D photonic crystal network structure and using resonant cavity. Alongside with reduction in crosstalk phenomenon by mean of -19.74 dB, also the average bandwidth Δλ of 0.2 nm and mean transmission range of 93.47%, the average value of quality factor 7829.25 was reached. In these calculations using finite difference time domain method (FDTD), optimized structures of 2D DWDM two-channel communication demultiplexer photonic crystals to reduce crosstalk phenomenon was obtained.
  • Mohammadreza Pashaei, Amir Rastegarnia Pages 57-61
    In this paper, to decrease of crosstalk phenomenon at de-multiplexer two-channel of optical communication, we designed a de-multiplexer two-dimensional (2D) photonic crystal (PhC) using resonant line defect cavity and by removing four defects. In this research, we reached to decrease in crosstalk phenomenon with mean of -24.681 dB in photonic crystal two-channel de-multiplexer according to ultra-narrow bandwidth mean of 0.25 nm and quality factor Q with ultra-average amount of 6546.5. PWE calculation methods were used to obtain band structure and photonic band gap and FDTD numerical calculation method was used to obtain output spectrum of photonic crystal two-channel de-multiplexer.
  • Javad Zeraatkar Moghaddam, Hamid Farrokhi Pages 63-70
    In this paper, we introduce a spatial MIMO channel for modern communication systems. Parameters required in the spatial MIMO channel modeling are studied and the channel is simulated for two types of modeling named “un-polarized” and “cross-polarized” antennas. Then, the channel capacity is computed at different signal to noise ratio. Besides, the channel capacity is analyzed for two different scenarios including high SNR and low SNR. To reach the maximum capacity, the optimal power allocation on antennas is also investigated. The simulation results show that, at low SNR, the power allocation to the sub-channel corresponding to maximum singular value is optimal and equal power allocation to the sub-channels is optimal at high SNR.
  • Azizollah Jamshidi, Samaneh Moezzi Pages 71-77
    Underwater acoustic communication is suffered from the channel effects which results in time spreading of the transmitted signal. In underwater environment multiple replicas of the transmitted signal are received at the receiver through different paths, which causes significant Inter-Symbol Interference (ISI). Decision Feedback Equalizers (DFE) was utilized to overcome this type of interference in digital communications so many years ago. However, because of the complexity of adaptive equalizers Passive Phase Conjugation (PPC) was widely exploited in underwater communications in the recent years. Because of the poor performance of the PPC method, adaptive equalizers are jointed to improve the PPC performance. In this paper, experimental results conducted in Shiraz Electronic Industrials’ pool are reported. Three different approaches are compared in terms of Symbol Error Rate (SER) versus the number of used channels at the pool: 1) the PPC method; 2) DFE equalizer for only a single channel; 3) the PPC method combined with adaptive DFE. The experimental results showed that the third approach outperforms the others while a simpler receiver is obtained.