نشریه صنایع الکترونیک
پیاپی 2 (تابستان 1389)

The current study was an attempt at designing and simulating a 17-element shaped-beam linear antenna array which works at 5 GHz and produces cosecant pattern in 25-degree beam width and different side lobe levels. The synthesis procedure was done by using Adaptive Nulling and improved Gradient Search Algorithm (GSA) optimization. Finally, having simulated the radiation pattern of the array, we found out that it was an appropriate step toward the desired pattern.

Until now, with assumption of equality of round functions of DESlike Block ciphers, several articles presented the Upper bound of the maximum differential probability. In this paper, we will present the upper bound on maximum differential probability for DES-like block ciphers with different round functions.

Quantum Cellular Automata (QCA) represents an emerging technology at the nanotechnology level. Because of high speed, nanoscale size and ultra low power nature of QCA, cryptography can be an interesting application of QCA technology. QCA implementation of the serpent block cipher is discussed in this paper. The basic modules of serpent are implemented using QCA cells. it can be obviously seen that the implementation of cryptographic algorithms in this technology has considerable advantages compared to conventional CMOS approach.

Metamaterial covers have unique electromagnetic properties which make them popular in the communication systems. The transmission phase curves of the conventional metamaterial covers are identical for a normally incident plane wave regardless of its X- or Y-polarization states. The aim of this work is to use a polarization dependent metamaterial cover to change the polarization state of the incident wave. Two novel polarization-dependent metamaterial (PDMTM) covers, which transmission phase curves for x- and y- polarizations are different, are proposed. A full-wave FDTD numerical technique is adopted for the simulations.

This paper presents a rigorous and comprehensive method for retrieving the electromagnetic constitutive parameters of a slab of metamaterial from the measurement or numerically calculation of scattering parameters. The main problem in this process is the doubtfulness exists in the phase of the transmitted field or the correct branch of logarithmic function appears in relevant equations.The novelty introduced here is on applying the Kramers-Kronig(K-K) relation to the imaginary part of refractive index and therefore obtaining its real part with less ambiguity. In Addition, by means of the mentioned approach one can obtain full retrieval results even where the imaginary part of electric permittivity or magnetic permeability becomes negative. Indeed, this method can be applied to an extensive range of materials independent of their operational frequency.

In wireless mobile channels, a major challenge in providing high-data rate spectral efficient communication link is to overcome the multipath propagation effect small-scale fading. Diversity techniques are widely used to reduce the effects of multipath fading and improve the reliability of transmission without increasing the transmitted power or sacrificing the bandwidth. In most wireless communication systems a number of diversity methods are used in order to get the required performance. According to the domain where diversity is introduced, diversity techniques are classified into time, frequency and space diversity.Depending on whether multiple antennas are used for transmission or reception, we can classify space diversity into two categories: receive diversity and transmit diversity. Space time coding is a type of transmit diversity. Space-time coding is a coding technique designed for use with multiple transmit antennas. Coding is performed in both spatial and temporal domains to introduce correlation between signals transmitted from various antennas at various time periods. There are various approaches in coding structures, including space-time block codes (STBC), space-time trellis codes (STTC), space-time turbo trellis codes and layered space-time (LST) codes. This paper aims to implement the encoder and Viterbi decoder for space-time trellis codes,at same time evaluate the performance of some space-time trellis codes, To gain more insight of the performa--nce of space-time codes, simulation was carried out over several types of fading channels, including flat Rayleigh/Nakagami fading and frequency selective fading channels.

Satellite networks of a field have been improving and flourishing since the first communicative satellite had been made. By the increase of the need for mobile communication in the future, Making wide bandwidth and global covering with a suitable and logical selected satellite are assumed to be beyond the ground capabilities. Therefore their network communication with ground network and protocols would consist the major part of networking the satellites. Amongst these things, having the sent information security created between the satellite and ground stations is really important. Firewall is one of the elements which provides security in the network. In this paper we are going to present a hardware firewall and it’s implementation with VHDL language on FPGA.We will show you that the designed system in this paper not only does have high speed and performance but also has both low power consumption and low utilized space. To increase the processing speed and reduce the signaling volume related to external memories, which are linked to FPGA are many times slower than the processing speed of FPGA, we have used and applied embedded memories of FPGA in this design, have mixed it with pipeline technique, so have reached a high performance within low power consumption. The advantages of this proposed architecture have solved the processing bottlenecks and have made it plausible to be used in the communicative satellites.