Do-Hoon Kwon

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

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Publications (55)82.73 Total impact

  • [Show abstract] [Hide abstract]
    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.
    IEEE Transactions on Antennas and Propagation 03/2014; 62(4). DOI:10.1109/TAP.2013.2297162 · 2.46 Impact Factor
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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.
    IEEE Communications Letters 02/2014; 18(2):317-320. DOI:10.1109/LCOMM.2013.122713.132588 · 1.46 Impact Factor
  • Do-Hoon Kwon, D.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.
    IEEE Transactions on Antennas and Propagation 01/2014; 62(1):153-162. DOI:10.1109/TAP.2013.2287515 · 2.46 Impact Factor
  • 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.
    2013 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting; 07/2013
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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.
    2013 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting; 07/2013
  • 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.
    2013 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting; 07/2013
  • 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.
    2013 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting; 07/2013
  • 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.
    IEEE Transactions on Antennas and Propagation 03/2013; 61(3):1327-1333. DOI:10.1109/TAP.2012.2227661 · 2.46 Impact Factor
  • 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.
    IEEE Antennas and Wireless Propagation Letters 12/2012; 11:1125-1128. DOI:10.1109/LAWP.2012.2218092 · 1.95 Impact Factor
  • 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.
    IEEE Transactions on Antennas and Propagation 09/2012; 60(9):4210-4218. DOI:10.1109/TAP.2012.2207032 · 2.46 Impact Factor
  • Do-Hoon Kwon, C.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.
    Antennas and Propagation (EUCAP), 2012 6th European Conference on; 01/2012
  • C.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.
    Antennas and Propagation Society International Symposium (APSURSI), 2012 IEEE; 01/2012
  • 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.
    Antennas and Propagation Society International Symposium (APSURSI), 2012 IEEE; 01/2012
  • C.D. Emiroglu, Do-Hoon Kwon
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    ABSTRACT: A transmission-line metamaterial design of a material-embedded line source radiating inside a ground recess is presented. The media embedding the recessed line source is designed such that the embedded current creates the same radiation pattern as a line source over a flat conducting ground plane. A numerical example based on circuit simulations is shown to validate the effectiveness of the embedded design at the design frequency.
    Antennas and Propagation (APSURSI), 2011 IEEE International Symposium on; 08/2011
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    ABSTRACT: Metamaterial lenses derived through transformation optics offer control over wave behavior and potential for new antenna structures. A collimating lens is presented with an embedded source that produces up to four orthogonal far-field beams based on the position of the source. As a feasibility confirmation, an example metamaterial design for the lens is presented. Another far-field collimating flat lens allows for fine beam scanning and potential for multiple beamforming based on the position of the sources behind the lens.
    Antennas and Propagation (EuCAP), 2010 Proceedings of the Fourth European Conference on; 05/2010
  • Source
    Caglar D. Emiroglu, Do-Hoon Kwon
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    ABSTRACT: Based on the coordinate transformation technique, a three-dimensional beam expander/compressor design is presented. Spatial coordinates in two orthogonal directions tangential to the device boundary are scaled at the same rate. The reflection and transmission coefficients are obtained in a closed form at the planar boundary for a plane wave illumination at an arbitrary incidence angle. The reflection and transmission characteristics under two-dimensional Gaussian beam illuminations are analyzed by constructing the incident, reflected, and transmitted waves as a superposition of plane wave components via Fourier transform. Numerical examples are provided to demonstrate the small amount of reflection compared with two-dimensional counterparts of the expander/compressor.
    Journal of Applied Physics 05/2010; DOI:10.1063/1.3383057 · 2.19 Impact Factor
  • Do-Hoon Kwon, D.H. Werner
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    ABSTRACT: The recently introduced transformation-electromagnetics techniques provide a new methodology for designing devices that possess novel wave-material interaction properties. They are based on the form invariance of Maxwell's equations under coordinate transformations. These methods provide an extremely versatile set of design tools that employ spatial-coordinate transformations, where the compression and dilation of space in different coordinate directions are interpreted as appropriate scalings of the material parameters. The most famous transformation-optics device is the cloak of invisibility. However, a wide variety of other devices are also possible, such as field concentrators, polarization rotators, beam splitters, beam collimators, and flat lenses. In this paper, an overview of transformation-electromagnetics device design techniques is presented. The paper begins by introducing the underlying design principle behind transformation electromagnetics. Several novel transformation-based device designs are then summarized, starting with electromagnetic cloaks that have spherical shell or cylindrical annular shapes, More general cloaking designs of noncircular annular geometries are treated, and the application of cloaking to RF/microwave antenna shielding is also discussed. Following this, device designs that employ transformations that have discontinuities .on the domain boundary are presented. Unlike those used for cloaks, this type of transformation is capable of modifying the fields outside of the device. Examples of this type of transformation-electromagnetics device are presented, which include flat near-field and far-field focusing lenses, wave collimators for embedded sources (e.g., antennas), polarization splitters and rotators, and right-angle beam benders.
    IEEE Antennas and Propagation Magazine 03/2010; 52(1-52):24 - 46. DOI:10.1109/MAP.2010.5466396 · 1.15 Impact Factor
  • Source
    Do-Hoon Kwon, Caglar D. Emiroglu
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    ABSTRACT: Using the coordinate transformation approach, low-profile material-embedded horizontal linear arrays are designed such that the embedded arrays perform identically to a vertical array of the same length in free space. A vertical array in free space is first rotated by a right angle using a transformation-based rotator. The height of the rotated array is subsequently reduced through a reflectionless compression procedure in the vertical direction. The resulting low-profile array can scan a narrow beam at large scan angles without having a broadening main beam, unlike a linear array in free space. Two transformation material designs are presented based on circular and square annular rotators. Numerical simulation results are provided to verify the scanning performance. The effect of material loss on the radiation pattern is examined numerically.
    Journal of Applied Physics 03/2010; 107(3-107):034508 - 034508-8. DOI:10.1063/1.3294647 · 2.19 Impact Factor
  • Do-Hoon Kwon
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    ABSTRACT: A radiation configuration is designed for a monopole antenna embedded within transformation media and buried inside a recess in a conducting ground plane. Both the ground plane near the base of the antenna and the antenna itself, which are physically located inside a recess, are mapped to a virtual location above the ground plane by a negative-index material block. The directivity pattern is identical to that of a monopole on a flat ground plane, radiating the maximum vertically polarized field in the horizon. Radiation characteristics are tolerant to small variations in material parameters from ideal values. Estimates for pattern and impedance bandwidths are provided based on numerical simulations.
    IEEE Antennas and Wireless Propagation Letters 02/2010; 9(9):432 - 435. DOI:10.1109/LAWP.2010.2049821 · 1.95 Impact Factor
  • Do-Hoon Kwon, Caglar D. Emiroglu
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    ABSTRACT: A thin low-profile embedded horizontal array design was presented based on the transformation electromagnetics methodology. By applying coordinate transformations to a conductor-backed vertical array in free space, an embedded horizontal array can scan a narrow beam in the angular range near the axial direction. The effect of material loss was investigated numerically. Metamaterials are the prime candidates for realizations. Loss in practical metamaterials will be a key factor in the effectiveness of the embedded horizontal array.
    01/2010; DOI:10.1109/APS.2010.5560993