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    Compact broadband printed monopole antenna

    , Article Applied Computational Electromagnetics Society Journal ; Volume 28, Issue 4 , 2013 , Pages 321-326 ; 10544887 (ISSN) Jafargholi, A ; Jafargholi, A ; Sharif University of Technology
    2013
    Abstract
    A compact printed monopole antenna for broadband application is presented. The proposed antenna, having a total physical size of 21 × 6.5 mm consists of a patch fed by a coaxial line and an SMA connector as partial finite ground plane. The modified patch plane with a slot in its feed point helps to increase the impedance bandwidth of the proposed antenna. The optimal design may offer an ultra-wide impedance bandwidth from 2.56 GHz to 20 GHz. A prototype is fabricated and tested. The agreement between the simulated and measured results is quite good  

    Design and fabrication of a new multi-loop saddle coil for 1.5 T MRI

    , Article Review of Scientific Instruments ; Volume 90, Issue 11 , 2019 ; 00346748 (ISSN) Parsa, J ; Mohammadzadeh, M ; Sharif University of Technology
    American Institute of Physics Inc  2019
    Abstract
    Radiofrequency coils provide high-resolution magnetic resonance (MR) imaging of human tissues. A small RF coil produces MR images with a higher resolution compared to the commercial volume MR coils from mass limited samples. Signal to noise ratio (SNR) plays a key role in the optimal design of receiver radiofrequency coils. In this work, we present a three-loop saddle coil suitable for MR imaging of digits of the human body. The geometry of the introduced coil is optimized to achieve the highest SNR. The coil performance is evaluated through comparing the measured SNR maps of the optimal coil derived from MR images of a saline phantom with the corresponding measured SNR maps of a commercial... 

    Beam profile and image transfer study in multimode optical fiber coupling

    , Article Journal of Applied Sciences ; Volume 8, Issue 22 , 2008 , Pages 4210-4214 ; 18125654 (ISSN) Asadpour, A ; Golnabi, H ; Sharif University of Technology
    2008
    Abstract
    In this study the optical beam transfer and imaging in an optical fiber coupling is discussed. In coupling two fibers, some measurements from intensity perspective are performed and intensity profile is investigated. A theoretical model for the power transmission in fiber coupling is developed and theoretical function is compared with the experimental results. The amount of light delivered to the receiving fiber depends on the acceptance angle of the receiving fiber and the core cross sections of both fibers. Intensity profile function obtained theoretically agrees well with the measured results. The intensity variation as a function of the air gap variation is investigated in this article.... 

    Coplanar waveguide-FED planar spiral antenna with integrated impedance transformer

    , Article Microwave and Optical Technology Letters ; Volume 55, Issue 6 , 2013 , Pages 1338-1341 ; 08952477 (ISSN) Vahidpoor, Z ; Forooraghi, K ; Fotowat Ahmady, A ; Atlasbaf, Z ; Sharif University of Technology
    2013
    Abstract
    A new planar spiral antenna with integrated impedance transformer is presented which needs no external balun and can be fed by a coplanar waveguide.The proposed structure has a return loss of <-10 dB over a broad bandwidth of 0.5-5 GHz that is suitable for cognitive radio applications. The effects of different spiral and transformer parameters are investigated through various simulations. A case of the proposed antenna is fabricated, and measurement results are presented including return loss, gain, and radiation patterns  

    Effect of geometry, joule heating, and critical current on the responsivity of MOD superconducting transition edge sensors

    , Article Journal of Superconductivity and Novel Magnetism ; Volume 26, Issue 4 , April , 2013 , Pages 831-834 ; 15571939 (ISSN) Hosseini, M ; Moftakharzadeh, A ; Kokabi, A ; Vesaghi, M. A ; Fardmanesh, M ; Sharif University of Technology
    2013
    Abstract
    By fabrication of several bolometric detectors on the YBCO film made of Metal-Organic Deposition (MOD) and the effect of pattering and film parameters on the optical responsivity of transition edge sensors is investigated. The low cost nonfluorine (MOD) method has been applied to fabricate YBCO thin films with different patterning parameters. The measurement results of the optical responsivity versus modulation frequency up to 100 KHz for these devices are reported  

    Radiation properties enhancement of a GSM/WLAN microstrip antenna using a dual band circularly symmetric EBG substrate

    , Article IEEE Transactions on Antennas and Propagation ; Volume 60, Issue 11 , 2012 , Pages 5491-5494 ; 0018926X (ISSN) Salarrahimi, M ; Rashed Mohassel, J ; Edalatipour, M ; Sharif University of Technology
    2012
    Abstract
    This communication presents a dual band circular patch antenna with improved radiation properties at GSM and WLAN frequency bands, i.e., 1.8 and 2.4 GHz. The improvement has been achieved using a dual band circularly symmetric EBG (CS-EBG) structure. The structure has been simulated, fabricated and measured demonstrating notable enhancement in antenna radiation patterns at both frequency bands. Results show 5 dB and 7 dB improvement in front to back ratio at design frequencies of 1.8 GHz and 2.4 GHz respectively. In addition, measurement results demonstrate 0.8 dB increase in antenna gain and significant reduction in cross polarization level at both frequency bands  

    Cooperative cyclostationary spectrum sensing in cognitive radios at low SNR regimes

    , Article IEEE International Conference on Communications, 23 May 2010 through 27 May 2010, Cape Town ; 2010 ; 05361486 (ISSN) ; 9781424464043 (ISBN) Derakhshani, M ; Nasiri Kenari, M ; Le Ngoc, T ; Sharif University of Technology
    2010
    Abstract
    The paper proposes efficient cooperative cyclostationary spectrum sensing schemes in which each secondary user (SU) performs single-cycle cyclostationary detection for fast and simple implementation, while collaboration between SUs in final decision on the presence or absence of the primary user (PU) is explored to improve its performance. As the SUs simultaneously measure the spectral correlation functions at different cycle frequencies (CF) and exchange their information regarding the measured results, a sufficient number of CFs are effectively examined in a short period of time because of parallel searching, which makes the proposed cooperative spectrum sensing more reliable and faster.... 

    Broadband omnidirectional and miniature fold-up discone antenna in VHF/UHF band

    , Article Electromagnetics ; Volume 32, Issue 5 , Jul , 2012 , Pages 266-273 ; 02726343 (ISSN) Javadzadeh, S. M. H ; Karkhaneh, H ; Sadeghpour, T ; Sharif University of Technology
    2012
    Abstract
    In this article, a novel miniature broadband omnidirectional antenna is proposed. This antenna is suitable to use in vehicles, especially in unmanned aerial vehicles, since it will be folded in order to reduce its size when the unmanned aerial vehicle lands. A special kind of wire discone antenna is chosen to achieve all desired goals. Passive broadband impedance matching at the input of the antenna improves the voltage standing-wave ratio. A telescopic fiberglass axis is used in the antenna structure in order to reduce size and increase wind resistance. The assessment of the novel structure in implementing the antenna is confirmed by experimental measurements. The measurement results reveal... 

    Wide-band spiral filter using microstrip patches to increase external and internal coupling

    , Article Electromagnetics ; Volume 32, Issue 3 , 2012 , Pages 161-172 ; 02726343 (ISSN) Roshanmanesh, S ; Javadzadeh, S. M. H ; Sharif University of Technology
    Abstract
    Microwave filters have successfully been miniaturized using spiral resonators. One of the typical problems in wideband microwave filters, such as spiral filters, is the need for very small gaps between resonators to accomplish high external and internal coupling. These gaps cause difficulties in the physical implementation of the filter, especially at high frequencies. To avoid this problem and to enable easy fabrication of the filter, a rectangular microstrip patch was used as a coupling capacitor instead of small gaps between resonators. This technique was used both for external and for internal coupling of the filter. Additionally, this approach has another important benefit; it removes... 

    Efficient cooperative cyclostationary spectrum sensing in cognitive radios at low SNR regimes

    , Article IEEE Transactions on Wireless Communications ; Volume 10, Issue 11 , 2011 , Pages 3754-3764 ; 15361276 (ISSN) Derakhshani, M ; Le Ngoc, T ; Nasiri Kenari, M ; Sharif University of Technology
    Abstract
    This paper proposes efficient cooperative cyclostationary spectrum sensing schemes in which each secondary-user (SU) performs single-cycle (SC) cyclostationary detection for fast and simple implementation, while collaboration between SUs in final decision on the presence or absence of the primary-user (PU) is explored to improve its performance. As the SUs simultaneously measure the spectral correlation functions at different cycle-frequencies (CF) and exchange their information regarding the measured results, a sufficient number of CFs are effectively examined with parallel searching, which makes the proposed cooperative spectrum sensing more reliable. This paper presents another look at... 

    A dual mode UHF EPC Gen 2 RFID tag in 0.18 μm CMOS

    , Article Microelectronics Journal ; Volume 41, Issue 8 , 2010 , Pages 458-464 ; 00262692 (ISSN) Najafi, V ; Mohammadi, S ; Roostaie, V ; Fotowat-Ahmady, A ; Sharif University of Technology
    2010
    Abstract
    A dual mode UHF RFID transponder in 0.18 μm CMOS conforming to the EPC Gen 2 standard is presented. Low voltage design of the analog and digital blocks enables the chip to operate with a 1 V regulated voltage and thus to reduce the power consumption. The novel dual mode architecture enables the chip to work in passive and battery-assisted modes controlled by the reader. A custom Gen 2 based command switches the operation mode of the circuit. By using a special clock calibration method the chip operates from 1.2 to 5 MHz clock frequency. Several low power techniques are employed to reduce the power consumption of the chip which is essential in passive RFID tags. Measurement results show that... 

    An energy efficient 40 Kb SRAM module with extended read/write noise margin in 0.13μm CMOS

    , Article IEEE Journal of Solid-State Circuits ; Volume 44, Issue 2 , 2009 , Pages 620-630 ; 00189200 (ISSN) Sharifkhani, M ; Sachdev, M ; Sharif University of Technology
    2009
    Abstract
    Based on the dynamic criteria for data stability, we introduce segmented virtual grounding architecture with extended read, write noise margin to realize a low leakage current, energy efficient SRAM module. The architecture offers subthreshold operation for the entire module, except for the selected segments. In addition, a new operational mode for the SRAM cell is introduced which allows only the bitlines of the selected columns to be discharged in an operation. The stability of the cells is enhanced in both read and write operation by controlling the cell access time and cell supply voltage, respectively. A 2048$, imes,$20 bit eSRAM unit is implemented in a regular 0.13 $muhbox{m} $ CMOS... 

    Asymmetrical 4×4 butler matrix and its application for single layer 8×8 butler matrix

    , Article IEEE Transactions on Antennas and Propagation ; Volume 67, Issue 8 , 2019 , Pages 5372-5379 ; 0018926X (ISSN) Tajik, A ; Shafiei Alavijeh, A ; Fakharzadeh, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Abstract
    The design procedure and measured results of a novel 4 × 4 Butler matrix are presented in this paper. This asymmetrical structure provides fairly flexible phase outputs; therefore, the array radiation pattern can be rotated around the array normal axis. The structure of this modified Butler matrix is discussed in detail, and the explicit design formulas are derived to achieve the arbitrary main beams direction. Using the proposed design procedure, the Butler matrix can provide even broadside and endfire beams. In addition, this structure is employed to design two Butler matrices, which generate similar patterns as a conventional 8 × 8 Butler matrix, using only single layer circuits with... 

    Calculation of eddy current losses caused by leads and other current sources in high current power transformerst

    , Article 2008 Australasian Universities Power Engineering Conference, AUPEC 2008, Sydney, NSW, 14 December 2008 through 17 December 2008 ; April , 2008 ; 9781424441624 (ISBN) Motalleb, M ; Vakilian, M ; Abbaspour, A ; Sharif University of Technology
    2008
    Abstract
    The leads with heavy current passing through the covering plates, and the winding in a transformer, are sources of eddy current losses. Due to this loss some regions of tank wall are subject to serious local overheating. It affects the safety and reliability of this expensive object and power delivery. In this paper these eddy current losses are calculated through a new formulation by application of Finite Element Method, using FEMLAB software. These results are compared with measurement results and the computational results of two other methods: the Turowski method and a method based on application of EDMAG software. © 2008 Australasian Universities Power Engineering Conference (AUPEC'08)  

    Effect of parametric instability on phase noise degradation in a varactor frequency multiplier

    , Article Asia-Pacific Microwave Conference, APMC 2007, Bangkok, 11 December 2007 through 14 December 2007 ; 2007 ; 1424407494 (ISBN); 9781424407491 (ISBN) Ahmadi, A ; Banai, A ; Sharif University of Technology
    2007
    Abstract
    Varactor frequency multipliers often show parametric instability with increasing RF input power. Examination of the added phase noise of the varactor frequency multipliers show that, if parametric oscillations are present in the circuit, output phase noise degrades remarkably in some specific driving levels. Phase noise analysis is done by the conversion matrix method. The conversion method predicts the phase noise degradation precisely because it encounters the noise conversion by large driving levels. The added phase noise of a varactor frequency doubler with subharmonic oscillation is calculated and the simulation results are compared with measurement results. Both simulation and... 

    A sub 1 v high PSRR CMOS bandgap voltage reference

    , Article Microelectronics Journal ; Volume 42, Issue 9 , 2011 , Pages 1057-1065 ; 00262692 (ISSN) Chahardori, M ; Atarodi, M ; Sharifkhani, M ; Sharif University of Technology
    2011
    Abstract
    A Bandgap circuit capable of generating a reference voltage of less than 1 V with high PSRR and low temperature sensitivity is proposed. High PSRR achieved by means of an improved current mode regulator which isolates the bandgap voltage from the variations and the noise of the power supply. A vigorous analytical approach is presented to provide a universal design guideline. The analysis unveils the sensitivity of the circuit characteristic to device parameters. The proposed circuit is fabricated in a 0.18μm CMOS technology and operates down to a supply voltage of 1.2 V. The circuit yields 20 ppm/°C of temperature coefficient in typical case and 50 ppm/°C of temperature coefficient in worst... 

    Single-VCO multi-band DTV frequency synthesizer with a divide-by-3 frequency divider for quadrature signal generation

    , Article Analog Integrated Circuits and Signal Processing ; Volume 64, Issue 2 , 2010 , Pages 103-113 ; 09251030 (ISSN) Saeedi, S ; Atarodi, M ; Sharif University of Technology
    Abstract
    A multi-band frequency synthesizer for In-phase and Quadrature (I/Q) LO signal generation in Digital TV tuners is presented. Using divisor numbers other than powers of 2 (2 n ) for quadrature generation, reduces the required frequency range of the VCO, hence the number of VCO circuits, in multi-band frequency synthesizers. In the proposed synthesizer, VHF, UHF and L-band frequencies are covered with only one VCO. This is achieved by using a novel divide-by-3 circuit which produces precise I/Q LO signals. The VCO tuning range in this design is 2,400-3,632 MHz which is covered by a 6-bit switched-capacitor bank. A fast adaptive frequency calibration block selects the closest VCO frequency to...