نشریه صنایع الکترونیک
سال دهم شماره 1 (پیاپی 37، بهار 1398)

In this paper, a fractional-N frequency synthesizer based on type-III phase locked loop (PLL) architecture is proposed for frequency modulated continuous wave (FMCW) radar systems. Analysis of the type-III PLL shows that it generates linear frequency ramps more accurately compared with its type-II counterpart and its steady-state phase error is zero, independent of the loop bandwidth and rate of the frequency variation. Considering the stability issues, power consumption, output phase noise and accuracy of the frequency ramp generation, design procedure of the type-III FMCW frequency synthesizer is presented in this paper. Based on this procedure, a fractional-N frequency synthesizer, which generates the triangular frequency sweep by a delta-sigma modulator, is designed at the center frequency of 10 GHz with frequency variation rate of 2 MHz/µs. Simulation results of the circuit, designed in a 0.18µm CMOS technology, illustrates that the frequency error is reduced by about 34% compared to the type-II PLL, designed at the same power consumption.

Reconfigurable antennas are capable of having several states of frequency response, polarization or radiation patterns. In order to benefit from this reconfigurability, we should choose the best state of antennas, regarding estimated values for communication channel. The main purpose of this work is to show capacity enhancement of a multi user multiple input multiple output (MU-MIMO) system by means of pattern reconfigurable antennas. Firstly, for a base station antenna array consisting of reconfigurable antenna elements and several single antenna users, an optimization problem is devised to find the best state in which system capacity is maximized. Afterwards, considering a 5×5 antenna array in the base station and 20 single antenna UEs, the achievable rate per UE versus SNR is obtained and plotted for non-reconfigurable to 5-state reconfigurable antenna elements. Based on these results, it is concluded that by means of reconfigurable antennas in the base station array, the achievable rate per user can be increased by 40% (0.045 bps/Hz) without beamforming and 5% (0.052 bps/Hz) with MRC beamforming.

In this paper, the magnetic field due to a current line source which is embedded inside a permeability (mu)and permittivity (epsilon) near zero or MENZ cylinder which has application in coherent propagation ofelectromagnetic field, has been studied. First, the analytical expressions of magnetic field are obtained forboth outside and inside of MENZ cylinder using wave equation. Then, it is demonstrated that the magneticfield inside the MENZ cylinder can be derived by using image theory. Closed-form expression of magneticfield inside the MENZ cylinder is derived by using the image theory. Finally, since it is for the first timethat the closed-form expression of magnetic field inside the MENZ cylinder for this structure is obtained,the derived formula is used as a benchmark to verify the numerical results of a finite element-basednumerical simulator. It is observed that the analytical and numerical results are in good agreement witheach other.

Bandwidth increment without changing the antenna size and thus with the compact size is one of the most important characteristics in the antenna design which has been taken into consideration during the recent years. In this paper, we present a sleeve antenna with a wide impedance bandwidth that consists of a coplanar waveguide (CPW) line connected to a metallic cylinder. The CPW line has been designed in non-uniform case to achieve the desire impedance matching. The effect of design parameters on impedance bandwidth is considered by some simulations. In addition of wide impedance bandwidth, the omnidirectional pattern, easy and low cast fabrication process and compact dimensions cause this antenna be a good choice for some military or radio frequency energy harvesting applications especially at low VHF/UHF frequency bands. In the field of radio frequency energy harvesting, the antenna with the patch structure can be used for energy harvesting in the GSM-900, GSM-1800 and UMTS-2150 bands along with the rectifier and the matching network. In this work the proposed antenna for frequency range of 185 to 523 MHz is simulated and compared with other previous works. The proposed antenna has a bandwidth of about 95.5% for a VSWR of less than 3 and compact size of "0.348λ"×"0.042λ" .

Different range-free algorithms are proposed for location estimation in Wireless Sensor Networks. In these algorithms, the network is assumed to have no error and false data. This paper attempts to model an attack and evaluate and analysis the effect of malicious data produced by node compromised attacks in some of the range-free algorithms: DV-hop, LSVM, NN and ELM. The false data may be produced by the malicious anchor nodes or compromised sensor nodes. The resistance of these algorithms against node compromise attacks is compared. The results show that although DV-hop has less localization error compared to the three other algorithms in a normal condition. However, LSVM and ELM, respectively, have less localization error in the case of beacon node compromise and sensor node compromise attacks. Further, in this research work, a new criterion is proposed for studying and comparing border problem issue in the localization algorithms. Using the simulation results from various algorithms outcomes has been used for comparison, where it can be considered that LSVM has better performance in the border problem compared with the other studied algorithms.

The efficiency of networks on chip (NoC) is affected by related routing algorithms. Network congestion has a negative impact on the performance of on-chip networks due to the increased packet latency. One of the key objectives design of NoC is reliability against failure. For a NoC to be robust, achieving better performance, and tolerating faults, two key functions need to be investigated: (a) the ability to avoid congested paths and balancing the traffic workloads, and (b) the ability to tolerate faults as well as proceeding to provide system functionality against physical impairment. For this purpose, a cost model for route selection with greater reliability and less congestion has been proposed. In this model, at first a congestion-aware routing algorithm is deployed based on the Q-learning approach to check congested areas in the network, then adjacent links are considered to deal with reliability. Finally, given the importance of the reliability, high weight is assigned to this parameter, and the path with the lowest cost is selected to forward packets. Simulation results show that the proposed approach outperforms state-of-the-art Bi-LCQ algorithm under two traffic patterns.

In this paper, a continuous-time (CT) third order multi standard low pass (LP) quadrature delta sigma modulator (QDSM) for low-IF receiver is designed. The proposed modulator is capable of supporting WLAN / WCDMA / GSM standards receivers at two real and quadrature mode. The adder Op-Amps at the end of the loop filter are eliminated to reduce the power consumption. This modulator is employed in real mode and single bit quantizer in GSM standard. To achieve the required bandwidth and SNR is worked in multi-bit quadrature mode in WLAN / WCDMA standards. The complex DAC (C_DAC) is designed to eliminate the mismatch between I and Q paths. This modulator is Implemented in 180 nm CMOS technology, and SNRs at transistor level are 54/ 75.9 / 81.63, and FOMs are 0.828 / 0.485 / 1.63 (pj / conv), for WLAN / WCDMA / GSM modes, respectively. The new structure has a better FOM at the WLAN / WCDMA operating modes compared to similar cases.

In this paper, a new broadband slim rectangular microstrip patch antenna with a narrow ground plane for GPS (1575.42 MHz), Glonass (1600 MHz), GSM (1800 MHz), LTE (1700 MHz), DAB (1452 MHz) and satellite phone (Iridium, 1616-1626.5 MHz; Inmarsat and Ligado, 1525-1646.5 MHz and Thuraya, 1525-1661 MHz) applications is proposed. The antenna is comprised of a slim rectangular patch, a shorting pin, a meander-line structure, and a defected ground plane. Its strip-like shape helps to be easily mounted inside the portable devices. The antenna has a dimension of approximately 0.43λ×0.02λ×0.008λ while achieving a gain and an efficiency of 2.4 dB and 95%, respectively. Using a defected ground plane the antenna impedance bandwidth (|S11|<−6 dB) of 32.6% from 1.44 to 2 GHz is observed. In order to validate simulation results, a prototype of the proposed printed antenna is fabricated and tested. Good agreement between the simulation and measurement results are obtained.