Do-Hoon Kwon

University of Massachusetts Amherst, Amherst Center, Massachusetts, United States

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Publications (65)87.06 Total impact

  • Do-Hoon Kwon · Hsieh-Chi Chang
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    ABSTRACT: For elements of an infinite planar phased array in free space, fundamental bandwidth bounds are derived from the optical theorem for periodic scatterers. The bounds are based on Gustafsson’s theory of fundamental bandwidth limits for electrically small antennas of arbitrary shape, but extended to periodic configurations. The element bandwidth bound is found to be a function of the strengths of the induced static dipole moments in constant background fields as well as the unitcell dimensions and the scan angle. Explicit bandwidth bound expressions are found for narrowband and ultrawideband array cases. They are numerically tested using example free-space array designs.
    No preview · Article · Aug 2015 · IEEE Transactions on Antennas and Propagation
  • Do-Hoon Kwon
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    ABSTRACT: For infinite planar phased array elements, a vector effective height is determined and the receiving area and receiving efficiency are found in terms of transmitting performance descriptors. The vector effective height allows the open-circuit received voltage to be expressed as an inner product with the incident electric field, as is for an isolated antenna. Generalizing a previously known expression, the effective area is expressed in terms of polarization mismatch, radiation efficiency, impedance mismatch, and the projected unit cell area, together with the element Floquet directivity introduced in this study that quantifies the unidirectional or bidirectional nature of radiation. An element’s total receiving efficiency is defined and its expression is inspected for maximizing the received power.
    No preview · Article · May 2015 · IEEE Transactions on Antennas and Propagation
  • Source
    M A Nikravan · Do-Hoon Kwon
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    ABSTRACT: A vertical E-plane waveguide-to-suspended stripline transition in the Ku band using a single dielectric substrate is presented. Inserting a resonator into the waveguide eliminates the need for a quarter-wave back-short. Using stacked patches as the resonator and increasing the separation between the resonator and the ground improve the bandwidth. A low transmission loss of 0.25 dB at 13.8 GHz and a 10-dB return loss bandwidth of 10% are achieved in simulation.
    Full-text · Conference Paper · Jul 2014
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    ABSTRACT: A wireless channel multiplexing method which utilizes both electric and magnetic field components of an electromagnetic wave as separate information carriers in the near-field region is presented. It is shown that multiplexing gain can be obtained in free space in the absence of scattering as well as indoor environments. Measured indoor channels at 1 MHz validate capacity enhancement of the proposed 2×2 MIMO link compared with the reference SISO link.
    Full-text · Conference Paper · Jul 2014
  • Do-Hoon Kwon · David M. Pozar
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    ABSTRACT: The exact radiation quality factor Q of infinite planar dipole arrays on a grounded magneto-dielectric substrate is presented. The radiated power and stored energies are evaluated in terms of Floquet modes and the spectrum of the arbitrary dipole current. The characteristics of Q with respect to geometrical and material parameters are shown. The Q of an array on a magnetic substrate can be lower than that of a similar array on a dielectric substrate.
    No preview · Conference Paper · Jul 2014
  • Hsieh-Chi Chang · Yong Heui Cho · Do-Hoon Kwon
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    ABSTRACT: The radiation quality factors of vertically and horizontally polarized single-mode dipole antennas over a ground plane are investigated and compared with their free-space counterparts. The theoretical Q results are validated using simulation and measurement results of small spherical helix dipole antennas. For vertically polarized antennas, the bandwidth can be enhanced approximately by a factor of two.
    No preview · Article · Mar 2014 · IEEE Transactions on Antennas and Propagation
  • Source
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    ABSTRACT: A wireless channel multiplexing method which makes use of the electric and magnetic field components of an electromagnetic wave as separate information carriers is presented. It is based on the observation that the rates of attenuation for electric and magnetic fields with respect to distance are different for electric and magnetic sources in the near-field region. Capacity enhancement is obtained in free space without any scattering. Measured indoor channels at 1 MHz confirm capacity enhancement of the proposed 2 x 2 MIMO link compared with the reference SISO link.
    Full-text · Article · Feb 2014 · IEEE Communications Letters
  • Douglas H. Werner · Do-Hoon Kwon
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    ABSTRACT: The articles in this special section present current and emerging research performed in the transformation electromagnetics (TE) area by the antennas and propagation community. The special section presents the latest research on this subject, including new applications as well as details on the design, simulations, fabricated implementation, and measurements of a variety of innovative TE devices.
    No preview · Article · Jan 2014 · IEEE Antennas and Wireless Propagation Letters
  • Do-Hoon Kwon · David M. Pozar
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    ABSTRACT: The exact stored energy, radiated power, and radiation quality factor of infinite planar phased arrays of dipole elements are presented for configurations in free space, over a ground plane, and on a grounded dielectric substrate. Radiated power and stored electric and magnetic energies are evaluated in terms of the two-dimensional spectral domain Floquet mode series representation of the element current. Characteristics of the radiated power and stored energies are clearly identified from propagating and evanescent spectra. In the presence of a ground plane, the dominant (0, 0) Floquet mode contributes to the stored energy, but not in the free-space case. Standard array configurations are analyzed, and the Q results are compared with impedance-derived values available by independent calculation.
    No preview · Article · Jan 2014 · IEEE Transactions on Antennas and Propagation
  • David M. Pozar · Do-Hoon Kwon
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    ABSTRACT: The energy storage and radiation quality factor of infinite planar phased arrays are studied for several cases of practical interest, including dipole arrays in free space and over a ground plane, as well as more general infinite phased arrays modeled with planar currents that excite only a small number of Floquet modes. The radiation Q is computed in a manner analogous to the classic Chu result for finite sized antenna elements [1], by calculating the stored electric and magnetic energies contained in a unit cell volume of the array (minus the energy density associated with the radiation field), and by calculating the radiated power from each unit cell. This is done using a full-wave moment method approach, with the appropriate Green's function for the geometry under consideration [2] (i.e., free-space, or over a ground plane). For lossless arrays in free space, in the absence of grating lobes, it is known that radiated power is contained only in the (0,0) Floquet mode, and that stored energy is contained only in higher order Floquet modes. This is in contrast to the Chu results for finite antennas, where each spherical wave mode contains some radiated power and some stored energy. The result is slightly different for arrays over a ground plane, where the (0,0) Floquet mode may contribute to the stored energies in the volume between the ground plane and the current elements. Both the radiated power and stored energies are evaluated in terms of the two-dimensional spectral domain Floquet mode series representation and the Fourier transform of the element current. Mode-by-mode correspondence of each Floquet mode contribution to the element input impedance is demonstrated, as is satisfaction of the complex Poynting theorem. The exact quality factor results are compared with approximate values based on the input impedance vs frequency from an independent calculation.
    No preview · Conference Paper · Oct 2013
  • Do-Hoon Kwon
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    ABSTRACT: Based on a forward scattering sum rule for a doubly periodic structure, fundamental limitation on the bandwidth of a free-space phased array element is derived. Expressions for bandwidth bounds are found in terms of the fractional bandwidth and the quality factor for wideband and narrowband responses. The derived bandwidth bound is numerically tested for a dipole array in free space.
    No preview · Conference Paper · Jul 2013
  • Yutong Yang · Do-Hoon Kwon
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    ABSTRACT: An indirect impedance measurement approach that does not require direct cable attachment using a two-port network is designed and numerically evaluated. Using a monopole as an interrogating antenna, the impedance of a small spherical helix dipole over a ground plane is retrieved. The accuracy and sources of error are discussed.
    No preview · Conference Paper · Jul 2013
  • Caglar D. Emiroglu · Do-Hoon Kwon
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    ABSTRACT: A microstrip transmission-line metamaterial design of a ground-recessed probe configuration for virtual source formation above the ground plane is presented. The effect of introducing a via hole for a shunt load is investigated. Virtual probe formation is validated using full-wave simulations.
    No preview · Conference Paper · Jul 2013
  • Hsieh-Chi Chang · Do-Hoon Kwon · Yong Heui Cho
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    ABSTRACT: Although the radiation quality factor of small antennas in free space has been investigated extensively in the past, the exact effect of a conducting ground plane on the antenna bandwidth is still not clearly understood. In this paper, radiation quality factors of vertically polarized antennas above a ground plane are computed and compared with their free-space counterparts. The theoretical Q result is validated with simulation of a small spherical helix antenna.
    No preview · Conference Paper · Jul 2013
  • Yong Heui Cho · Do-Hoon Kwon
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    ABSTRACT: Based on a common-area concept and insertion of an infinitesimal perfect magnetic conductor (PMC) wire, a new mode-matching method for mixed coordinate systems is proposed for the analysis of periodic magnetodielectric, perfect electric conductor, and PMC circular cylinder arrays. Our scattering solutions were computed and they showed favorable agreements with other known results in terms of power scattering coefficients, resonant frequency of nanostructures, and the sum rule of extinction width. The low-frequency solutions of periodic arrays were also formulated and compared with the full-wave counterparts.
    No preview · Article · Mar 2013 · IEEE Transactions on Antennas and Propagation
  • Do-Hoon Kwon
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    ABSTRACT: Based on quasi-conformal coordinate transformation, lens designs for conformal array antenna applications are presented. Potentially over a broad bandwidth for the two-dimensional TE polarization, a physically linear array can be transformed into a virtual curved array, or vice versa, using a lens having only nonmagnetic medium parameters. Lens designs for transforming between linear and cylindrical arrays in conformal conducting ground planes as well as their predicted scanning performances are shown. Such lenses can be designed and applied to existing array antennas to enable new scanning capabilities.
    No preview · Article · Dec 2012 · IEEE Antennas and Wireless Propagation Letters
  • Do-Hoon Kwon · Caglar Dogu Emiroglu
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    ABSTRACT: Characteristics of two-dimensional metamaterials based on non-orthogonal grids of transmission lines are investigated. From periodic analysis on a unit cell, the dispersion function is derived and compared with the orthogonal grid case. Isomorphism between Kirchhoff's circuital laws and two-dimensional Maxwell's equations is utilized to characterize the effective medium parameters. It is shown that a non-orthogonal grid structure is effective in realizing two-dimensional full-tensor anisotropic medium parameters in a simple geometrical configuration. For verification, a design example is provided where a probe current radiates near a planar interface between two anisotropic media and the results are compared with the analytical solution.
    No preview · Article · Sep 2012 · IEEE Transactions on Antennas and Propagation
  • Caglar D. Emiroglu · Do-Hoon Kwon
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    ABSTRACT: Dichroic frequency selective surface having stable filtering characteristics over a wide range of incidence angle is designed. The resonator layer is first represented by a homogeneous material slab using effective medium parameters. An optimal quarter-wave superstrate layer is subsequently applied. Angularly stable filtering responses are confirmed with simulation results.
    No preview · Conference Paper · Jul 2012
  • Do-Hoon Kwon
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    ABSTRACT: A sum rule for horizontal thin-wire dipole antennas backed by a perfectly conducting ground plane is presented. It is an integral identity for the extinction cross section of a conducting dipole multiplied by a weight function under a linearly polarized plane wave illumination. The weighted integral is found to be proportional to the static polarizability of the original and image dipoles in free space.
    No preview · Conference Paper · Jul 2012
  • Do-Hoon Kwon · Caglar D. Emiroglu
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    ABSTRACT: Using a coordinate transformation on a folded geometry, appropriate transformation media can make an embedded antenna appear as if it is positioned at a virtual location. For the TE polarization in two dimensions, embedding media for an electric line source are designed in transmission-line and inclusion-based resonant metamaterial configurations. For a line source positioned inside a recess in a conducting ground plane, the metamaterials are specifically designed to form a virtual line source above the ground plane. Metamaterial design details and simulation results for predicted radiation patterns are presented.
    No preview · Conference Paper · Mar 2012