JOURNAL OF IRANIAN ASSOCIATION OF ELECTRICAL AND ELECTRONICS ENGINEERS
Year:2020 | Volume:16 | Issue:4 |Papers Count:15

In this paper, a simple method for the discretization of planar continuous current sources is presented. First, the planar current distribution is determined by the Fourier and Inverse Hankel Transforms. Then it is discretized for the design of a planar array. The radiation pattern of the array of discrete elements will be quite different from that of the planar continuous current source. Therefore, for the improvement of its radiation characteristics, such as side-lobe level and ripple in the pattern, the iterative method of least squares is used. The desired radiation characteristics of the array, such as​ ​ the side-lobe level and ripple of pattern, are achieved by an iterative algorithm of the method of least squares together with the array element excitations. Indeed, first, in each iteration, in order to properly adjust the radiation pattern, the values of radiation pattern at the maximum points of the side-lobes and at the maximum and minimum points of the main-lobe, are replaced with the desired values. Then, by sampling of the adjusted radiation pattern, a linear equation system is obtained which by solving this linear equation system by using the method of least squares, the excitation currents of array elements are determined. The proposed method can be used to optimize any array with arbitrary configuration. Several examples of simulations have been presented to verify the efficacy of the proposed method.

In this paper, we present a new rule of antenna fix frequency beam scanning that scan the beam without using of phase shifters. We present antenna beam scanning by changing of surface impedance in Metallic leaky wave antenna. Our leaky wave antenna in this paper is Metallic corrugated leaky wave antenna that Surface impedance of this antenna controlled by height or gap distance of cogs and varies the basic parameter of leaky wave antenna for scanning the antenna main beam. With 1. 5mm cog’ s heights varying in 10GHz, the antenna main beam sweep 25 degree of space from 11 degree to 36 degree.

In this paper, Design and simulation of 4×4 Butler matrix in 2. 45 GHz is proposed. This network is utilized to feed of phased array antenna in order to create patterns in proper direction of space. The Butler matrix is designed on FR4 substrate by 125×113×0. 5 mm dimensions. To enhancing the bandwidth, improved microstrip passive elements such as directional branch-line hybrid coupler, cross over and Schiffman phase shifter are used. In the proposed design, isolation of 20-25dB at the central frequency is achieved, and outputs phase differences are coinciding to Butler matrix theory. The resulting bandwidth of ± 10º phase response is more than 10% in the central frequency.

In this paper, a novel ultra-wideband dipole antenna with a simple structure and low cost is presented. The impedance bandwidth (S11≤ 10 dB) of the proposed antenna is (1. 2_4. 55GHz) 116%. The whole of S-band frequency (2_4GHz) is covered completely and a part of L, C frequency bands are enveloped. The minimum and maximum gains in operation bandwidth are 2. 48dBi and 7. 48dBi respectively. The 50-ohm coaxial cable is utilized for feeding the antenna. To eliminate the backflow of the antenna and impedance matching with the coaxial transmission line, a Bazooka balun is adopted. Analysis of the current distribution and electric and magnetic fields on the dipole element have been conducted. A prototype of the antenna is fabricated and return loss, gain and radiation pattern are simulated and measured. The simulation and measurement parameters are suitable agreement.

A compact multiple-input– multiple-output (MIMO) antenna is presented for Long Term Evolution (LTE) applications. The antenna consists of a common square patch for ports and two ground plane with two separated microstrip feed lines. The antenna feed lines are placed perpendicularly to each other to obtain high isolation, and a T-shaped slot is added to reduce the mutual coupling of antenna elements in the operating frequency band. In this design two L-shaped radiator-elements are used for exiting two resonance frequencies that have connected to the patch by two metalized vias. The proposed MIMO antenna has a compact size of 38×37. 5 mm, and the antenna prototype is fabricated and measured. The measured results show that the proposed antenna design achieves an impedance bandwidth of larger than 1. 92– 2. 67 GHz for port-1 and 1. 69-2. 96 GHz for port-2, low mutual coupling of less than 10 dB, and a low envelope correlation coefficient across the frequency band, which are suitable for portable LTE applications.

In this paper, a Blumlein pulse forming line was modeled by echo phenomena in voltage transient wave in transmission lines. The effects of parameters disturbance were studied on output voltage pulse. These parameters are radius of connector, load impedance, line dielectric. Then an optimal line was designed for having a sharp pulse. The genetic algorithm was applied for line parameters optimization. The model parameters were validated by comparison output pulse with a real line and ideal pulses. The output pulses of the system have many applications in industrial, environmental, medical and military.

In this paper, a Multiple Coupled CMOS LC Quadrature Oscillator (MC-QO) in order to generate quadrature signals with a favorable phase noise and low power consumption is presented. In this work, the core of oscillator is coupled by the different passive and active coupling techniques in each stage. The active dynamic current-clipping technique is applied in the active coupling network, which can provides phase shift alone and results into the phase error and phase noise corrections of output signal. However, the passive coupling technique is also used in order to increase the corrections further. The passive coupling network consists of one RLC filter that besides the inherent reduction of noise, it provides compensating phase for reducing the resonator phase shift (RPS) in order to improve phase noise, which is proven by the analysis results. Using two coupling paths has a big contribution for increasing the coupling factor’ s value, which leads to the improvement of output’ s phase accuracy. Meanwhile, the passive coupling network does not dissipate additional power. Moreover, the applied tail current-shaping technique in the source of tail current causes the improvement of circuit’ s performance. To confirm the validity of the proposed quadrature oscillator’ s performance and the presented analysis, the MC-QO is simulated in TSMC 0. 18RF-CMOS technology at 3. 38 GHz fundamental frequency. The power consumption is 4. 6 mW from 1. 8 V power supply, the phase noise is-128. 2 (dBc/Hz) @ 1MHz and-138. 5 (dBc/Hz) @ 3 MHz offset frequencies with the quality factor (Q10. 8). Eventually, the excellent Figure of Merit (FOM) of-192. 25 (dBc/HZ) at 1 MHz offset frequency is achieved.

In this paper, design and implementation of a multi-standard quadrature delta-sigma modulator (QDSM) with a new structure is presented. This third order, FF, continuous time (CT), low pass (LP) QDSM is designed to supported the WLAN/WCDMA/GSM standards in low-IF receivers. The modulator is operates at single-bit real state in GSM mode and-to achieve the required bandwidth and SNR-multi-bit quadrature state in WLAN/WCDMA modes. To remove the DACs errors between I and Q paths, the DACs are designed to complex. Implemented in 180-nm CMOS, the modulator achieves 54/75. 9/81. 63 dB SNR and 1. 63/0. 6/0. 824 (pj/s Walden FoM) (131. 06/163. 35/156. 24 dB Schreier FoM) FOM for WLAN/WCDMA/GSM operating modes respectively.

A reciprocal dual-band BALUN is designed by the series connection of a multi-stage Wilkinson power divider and a 180° phase shifter. The use of the word “ reciprocal” is due to the fact that if the unbalanced input and balanced outputs are replaced, it also has a proper performance. As a proof of concept, a prototype model is fabricated and measured. The return loss is less than 10dB in the frequency bands 2. 5 to 5. 5 GHz and 10. 1 to 13 GHz. The isolation between the balanced ports is better than-15dB. Simultaneously, the unbalance between the amplitudes and phases of balanced ports is less than 0. 6 dB and, respectively. This BALUN is designed appropriately for TV satellite downlink.

An improvement in linearity of LNA amplifiers is achieved in proposed paper using auxiliary path, paralleled with the main amplifier. Moreover a cascode structure is employed to reach better amplifier parameter. Phase and amplitude are set through the second path and additional inductances in this transistor Source. Consequently non-linearity coefficient is controlled which leads to minimize the overall non-linearity coefficient. An investigation is also conducted on second-order non linearity coefficient which directly influences on IIP3. Power analyses can be used for it buta volterra analysis is applied for more accuracy and better nonlinearity modeling. DS method which is proposed in this paper can be added to various amplifier circuits since it parallels with the main circuit. Noise figure is controlled since the gates of transistors are not connected together directly. In this case we have reached an appropriate linearity which was anticipated the simulation results show a gain of 18dB, a noise figure of 2. 43dB, and an IIP3 of 7. 5dBm. All simulations are carried out using in 0. 18 µ m TSMC-RF technology.

Compared with wired networks, wireless networks have more practical features. One of the main problems in wireless channels is fading, in which the channel changes randomly that results in degrading the performance of the wireless system. One solution to deal with this effect is using cooperative communication. Using relays increases the coverage and the capacity of the network and reduces the power consumption. Moreover, the efficient use of the radio spectrum has introduced another subject called cognitive communication in which the available spectrum is used more efficiently. Cooperative cognitive radio networks have cooperative and cognitive radio networks properties. Cooperation is used in the spectrum sensing and in helping to send the primary user data in cognitive radio networks which improves the network performance. Besides, the new generation of telecommunication and mobile systems require high capacity and lots of energy due to the large amount of information traffic. Therefore, one of the issues discussed in this field is how to supply the energy of the system. Supplying the consuming energy by charging or replacing the energy source has always been problematic and costly. Thus, the harvested energy from the environment and especially the radio frequency signal can resolve this problem in communication systems. Using cooperative systems and cognitive radio networks with energy harvesting capability can improve the system performance. In this paper, a system model for cooperative cognitive radio networks with energy harvesting capability is proposed. In the proposed system model, one of the secondary users is selected as a relay to send the primary user information and all the secondary users harvest energy from the radio frequency signal. Mathematical analysis and simulation of the outage probability of the primary and secondary users are investigated. Moreover, the available parameters and their impact on the proposed model are discussed. Impact of relay selection methods, cognitive radio multi-user systems on the proposed model have been investigated.

Cognitive radio network is one of the proposed solutions to handle the scarcity of spectrum in the wireless communications systems. Spectrum sensing is the key step in the cognitive radio implementation and any problem in this functionality leads to the severe degradation in network performance. In this paper, a smart attacker is introduced which during the sensing period time, senses the spectrum and whenever primary user leaves, enters to channel. Then by emulating the behavior of the primary user, the attacker tries to reduce the spectral efficiency. We model the primary user and smart primary user emulation attacker traffics by a time dependent Markov process. By calculating the performance of the cognitive radio network and throughput of secondary user’ s network in the presence of the smart primary user emulation attacker, the impact of the traffic parameters over such performances are evaluated. Also launching primary user emulation attack in conventional and smart attacking methods are compared. The simulation results demonstrate that in the case of smart attacking, the throughput of the secondary user’ s network degrades considerably and if the appropriate attack traffic parameters are chosen, throughput might get close to zero.

In this paper, we investigate the physical layer security performance of a buffer-aided cognitive relay network over Rayleigh fading channels, where an underlay cognitive radio system is employed. In this network, a cognitive transmitter communicates with a cognitive receiver through a buffer-aided relay, in the presence of an eavesdropper overhearing the transmitted information. To evaluate the secrecy performance of the system, secrecy outage probability (SOP) has been used as a popular performance metric, where a closed-form expression is obtained. Numerical results obtained from the derived SOP expression, along with the Monte-Carlo simulation results are provided to evaluate the secrecy performance of the system under different system parameters. In addition, the secrecy performance of the system without buffer is evaluated and compared with that of the buffer-aided system. Assuming that the delay caused by buffer is negligible, it is shown that increasing the buffer size from L=2 to L=20 leads to a decrease in SOP from 10-2 to 10-3, indicating a performance improvement in the order of about 10. Moreover, buffer-aided relay system achieves 3 dB SNR gain compared to the performance of the system without buffer, at the SOP of 10-3.

In this paper, the pricing and bandwidth allocation in heterogeneous wireless access networks is studied. Demand modeling and resource allocation in heterogeneous wireless access networks is carried out using the theories of microeconomics in competitive markets. A competitive market model for bandwidth allocation and pricing is presented where new relaxation models and propositions are developed to address various aspects of the operation of wirless access networks such as roaming and hand off control. We used the existing market theories to develop a solution for pricing of a unit of bandwidth of each network based on the marginal cost of the product. The client preferences with regard to available networks are also modeled in our network market model. On the other hand, network providers also adjust their product offering according to the market price. We prove that the user and bandwidth assignment made on the basis of this model where all agents have rational behavior is Pareto optimum that maximizes the utility of networks and clients.