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    Wideband and polarisation-independent antireflection coating using metamaterials

    , Article IET Optoelectronics ; Volume 14, Issue 5 , 2020 , Pages 266-273 Sepehripour, F ; Karimi, P ; Khavasi, A ; Sharif University of Technology
    Institution of Engineering and Technology  2020
    Abstract
    Here, the authors propose a new approach for realising wideband and polarisation-independent antireflection coating, based on a metamaterial composed of a subwavelength array of metallic pillars with a square cross-section. The effective impedance of the array can be duly adjusted by the size and distance of the pillars. As such, the authors design the effective impedance of the antireflection coating to be the geometrical mean of the impedance of upper and lower media and choose its height to be quarter of operating wavelength. Doing so, the reflection vanishes at the desired frequency and fractional bandwidth of 56% is achieved with a criterion of 10% reflectance (the refractive index of... 

    A time modulated array with polarization diversity capability

    , Article IEEE Access ; Volume 9 , 2021 , Pages 53735-53744 ; 21693536 (ISSN) Mazaheri, M. H ; Fakharzadeh, M ; Akbari, M ; Safavi Naeini, S ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2021
    Abstract
    The Time Modulated Array (TMA) provides multiple radiation beams at different frequencies, by turning the radiating elements on and off. In this paper, we propose to add polarization diversity to a wireless communication link by leveraging the capabilities of the TMA. The proposed architecture switches between two orthogonal polarizations, instead of turning the antenna off, providing polarization diversity for the receivers. We show that the beams of each polarization at the sidebandsare exactly the same. However, the switching sequence should be optimized for the fundamental frequency to provide the same radiation level at each sideband. Two different switching sequences are proposed,... 

    Wide-band/angle blazed dual mode metallic groove gratings

    , Article IEEE Transactions on Antennas and Propagation ; 16 June , 2020 Hemmatyar, O ; Abbassi, M. A ; Rahmani, B ; Memarian, M ; Mehrany, K ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2020
    Abstract
    A simple approach to acquire wide-band/angle blazing operation in one-dimensional metallic gratings is investigated by means of mode-matching and equivalent circuit analysis. The gratings are single-groove perfectly conducting gratings that support two propagating guided modes (opposed to typical single mode cases). It is shown under what conditions, one can achieve blazing over a wide range of frequencies and angles. Most importantly, it is identified what governs blazing, in particular the true matching condition that needs to be satisfied, and how the structures’ multiple resonances play role in achieving such matching and tailoring the bandwidth. Parameters of the proposed equivalent... 

    Wide-band/angle blazed dual-mode metallic groove gratings

    , Article IEEE Transactions on Antennas and Propagation ; Volume 69, Issue 1 , 2021 , Pages 379-386 ; 0018926X (ISSN) Hemmatyar, O ; Abbassi, M. A ; Rahmani, B ; Memarian, M ; Mehrany, K ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2021
    Abstract
    A simple approach to acquire wide-band/angle blazing operation in 1-D metallic gratings is investigated by means of mode-matching and equivalent circuit analysis. The gratings are single-groove perfectly conducting gratings that support two propagating guided modes (opposed to typical single-mode cases). It is shown under what conditions one can achieve blazing over a wide range of frequencies and angles. Most importantly, it is identified what governs blazing, in particular the true matching condition that needs to be satisfied, and how the structures' multiple resonances play role in achieving such matching and tailoring the bandwidth. Parameters of the proposed equivalent circuit model... 

    Direct coupled resonator filters realized by gap waveguide technology

    , Article IEEE Transactions on Microwave Theory and Techniques ; Volume 63, Issue 10 , August , 2015 , Pages 3445-3452 ; 00189480 (ISSN) Ahmadi, B ; Banai, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    Abstract
    Novel types of narrow band filters based on the newly introduced gap waveguide technology are presented in this paper. The proposed filters have a central frequency of 35 GHz with approximately 1% fractional bandwidth. The filter resonators are composed of two separate plates and are manufactured by milling metallic blocks. The gap between the two metallic plates eliminates the need for electrical contact between them. This feature allows the resonators to be stacked in different layers. The filtering function is realized by producing a coupling between the stacked resonators. The measurement results of the manufactured filters are in good agreement with full-wave simulations, even without... 

    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...