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  • 1.
    Jonsson, B. Lars G.
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Shi, Shuai
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wang, Lei
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Ferrero, Fabien
    Lizzi, Leonardo
    On Methods to Determine Bounds on the Q-Factor for a Given Directivity2017In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 65, no 11, p. 5686-5696Article in journal (Refereed)
    Abstract [en]

    This paper revisit and extend the interesting case of bounds on the Q-factor for a given directivity for a small antenna of arbitrary shape. A higher directivity in a small antenna is closely connected with a narrow impedance bandwidth. The relation between bandwidth and a desired directivity is still not fully understood, not even for small antennas. Initial investigations in this direction have related the radius of a circumscribing sphere to the directivity, and bounds on the Q-factor have also been derived for a partial directivity in a given direction. In this paper, we derive lower bounds on the Q-factor for a total desired directivity for an arbitrarily shaped antenna in a given direction as a convex problem using semidefinite relaxation (SDR) techniques. We also show that the relaxed solution is also a solution of the original problem of determining the lower Q-factor bound for a total desired directivity. SDR can also be used to relax a class of other interesting nonconvex constraints in antenna optimization, such as tuning, losses, and front-to-back ratio. We compare two different new methods to determine the lowest Q-factor for arbitrary-shaped antennas for a given total directivity. We also compare our results with full electromagnetic simulations of a parasitic element antenna with high directivity.

  • 2.
    Shi, Shuai
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Wang, Lei
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    On Q-Factor Bounds for a Given Front-to-Back Ratio2017In: 2017 IEEE Antennas and Propagation Society International Symposium, Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 151-152Conference paper (Refereed)
    Abstract [en]

    In this paper, the goal is to solve an antenna current optimization problem minimizing the stored energy with a desired front-to-back ratio. This minimization problem is non-convex, and we use semidefinite relaxation techniques to find the solution. An initial study on the front-to-back ratio of a dipole shape is presented here.

  • 3.
    Wang, Lei
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. Ecole Polytechnique Fédérale de Lausanne, Switzerland.
    Jonsson, B. Lars G.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Mosig, J. R.
    Wideband omnidirectional planar antenna with vertical polarization2017In: 2017 11th European Conference on Antennas and Propagation, EUCAP 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 3865-3868, article id 7928581Conference paper (Refereed)
    Abstract [en]

    In this paper we propose a circular leaky wave-antenna with omnidirectional radiation in the H-plane. The design utilizes double-layered strips to create an end-fire antenna. A linear tapering of the stripes in the design endows the antenna with a 27% impedance bandwidth of 26.4-34.6 GHz. The antenna is vertically polarized with a cross polarization below -30 dB. The antenna has low gain variation in H-plane and it is compact as a planar structure. Furthermore, it can be easily fabricated and integrated by standard PCB processing techniques, which is very promising for applications such as base stations for wireless communication, spectrum monitoring and jamming systems.

  • 4.
    Wang, Lei
    et al.
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Yin, Xiaoxing
    Esquius-Morote, Marc
    Zhao, Hongxin
    Mosig, Juan R.
    Circularly Polarized Compact LTSA Array in SIW Technology2017In: IEEE Transactions on Antennas and Propagation, ISSN 0018-926X, E-ISSN 1558-2221, Vol. 65, no 6, p. 3247-3252Article in journal (Refereed)
    Abstract [en]

    Typical linearly tapered slot antenna (LTSA) usually features a wideband and a high gain. However, its geometry size is large, especially very long in the tapering direction, which limits its application in compact antenna and array systems. This communication has minimized the tapered length to less than 0.19 lambda(0) when the aperture width is less than 0.35 lambda(0) both for horizontally and vertically polarized LTSA arrays. Moreover, the typical polarization of the LTSA is linear, which is perpendicular to the slot. In this communication, an X-band circularly polarized 1x8 LTSA array, made of cross-LTSAs, is proposed with the feeding of a substrate integrated waveguide horn. All the three different polarized LTSA arrays are designed and investigated both in simulation and experiment, and the simulation results agree well with the measured results.

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