• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.9
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• pp.985-991
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• 2008

This paper presents a novel balanced mixer receiver front-end design based on a metamaterial structure applicable to differential-/common-mode excitation. This metamaterial structure functions as a leaky-wave antenna and provides in-trinsic common-mode suppression. Low LO leakage and high RF to LO isolation are achieved without additional filters for LO and RF paths. The metamaterial is based on a unit-cell which under a differential-mode excitation behaves like a composite right/left-handed(CRLH) metamaterial. In contrast, the metamaterial unit-cell is below cut-off under a common-mode excitation. Experimental results are used to verify the proposed metamaterial's differential-/common-mode characteristics. The metamaterial is integrated with a balanced mixer design resulting in an operation frequency range of $1.96{\sim}2.40$ GHz with an optimum mixer conversion loss of 21.1 dB at 2,4 GHz.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.146-147
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• 2000

The electromagnetic wave scattering from active objects has only recently attracted attention.$^{(1).(3)}$ Theoretical studies have considered normal-incidence plane-wave interactions with active dielectric cylinders with the prediction of large enhancements in the scattered field for bound mode structures. According to the theory of the electromagnetic wave scattering from a dielectric cylinder, the eigenvector solutions are discrete and have both guided (non-radiative) and leaky (radiative) mode solutions. By using an anti-guiding (leaky) structure instead of a guided structure and scattering at oblique incident angles near critical angle, the scattering resonances predicted by theoretical studies were obtained for the first time. A fine-grained scan of the plane-wave incident angle a reveals the existence of discrete scattering resonances. The diameter and real part of the index of refraction determine the resonant conditions and the imaginary part of the refractive index has a threshold value to make mode up for its radiation loss. The cross coupling between transverse electric (TE) and transverse magnetic (TM) modes is clearly detected for both active and passive scattering as theoretically expected. (omitted)

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.76.1-76.1
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• 2015

Optical resonances of metallic or dielectric nanoantennas enable to effectively convert free-propagating electromagnetic waves to localized electromagnetic fields and vice versa. Plasmonic resonances of metal nanoantennas extremely modify the local density of optical states beyond the optical diffraction limit and thus facilitate highly-efficient light-emitting, nonlinear signal conversion, photovoltaics, and optical trapping. The leaky-mode resonances, or termed Mie resonances, allow dielectric nanoantennas to have a compact size even less than the wavelength scale. The dielectric nanoantennas exhibiting low optical losses and supporting both electric and magnetic resonances provide an alternative to their metallic counterparts. To extend the utility of metal and dielectric nanoantennas in further applications, e.g. metasurfaces and metamaterials, it is required to understand and engineer their scattering characteristics. At first, we characterize resonant plasmonic antenna radiations of a single-crystalline Ag nanowire over a wide spectral range from visible to near infrared regions. Dark-field optical microscope and direct far-field scanning measurements successfully identify the FP resonances and mode matching conditions of the antenna radiation, and reveal the mutual relation between the SPP dispersion and the far-field antenna radiation. Secondly, we perform a systematical study on resonant scattering properties of high-refractive-index dielectric nanoantennas. In this research, we examined Si nanoblock and electron-beam induced deposition (EBID) carbonaceous nanorod structures. Scattering spectra of the transverse-electric (TE) and transverse-magnetic (TM) leaky-mode resonances are measured by dark-field microscope spectroscopy. The leaky-mode resonances result a large scattering cross section approaching the theoretical single-channel scattering limit, and their wide tuning ranges enable vivid structural color generation over the full visible spectrum range from blue to green, yellow, and red. In particular, the lowest-order TM01 mode overcomes the diffraction limit. The finite-difference time-domain method and modal dispersion model successfully reproduce the experimental results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.2
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• pp.259-267
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• 1997

The advent of B-ISDN using ATM(asynchronous transfer mode) made possible a variety of new multimedia services, however it also created a problem of congestion control due to bursty nature of various traffic sources. To tackle this problem, UPC/NPC(user parameter control/network parameter control) have been actively studied and DRLB(dynamic rate leaky bucket) algorithm, in which the token generation rate is changed according to states of data source andbuffer occupancy, is a good example of the UPC/NPC. However, the DRLB algorithm has drawbacks of low efficiency and difficult real-time implementation for bursty traffic sources because the determination of token generation rate in the algorithm is based on the present state of network. In this paper, we propose a more plastic and effective congestion control algorithm by combining the DRLB algorithm and neural network based prediction to remedy the drawbacks of the DRLB algorithm, and verify the efficacy of the proposed method by computer simulations.

• Journal of Satellite, Information and Communications
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• v.2 no.2
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• pp.10-15
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• 2007

Small size and low profile antenna for mobile vehicular-top-mounted is needed in satellite communication services such as DBS, Satellite Internet and VSAT. In middle latitudes, the development of an array antenna which has the conformal, low profile and 45 degree beam tilted configuration, and has the high gain with sharp beamwidth, low sidelobe and low loss is required for Ku-band satellite communication. In this paper, in order to meet with these performances, an array antenna consisting of the vertical polarized waveguide longitudinal slots based on the leaky-wave mode of traveling wave antenna is proposed. An array antenna consisting of 16 leaky-wave elements is showing 30 dBi of gain, 4.9 degree of beamwidth, below than -20 dB of sidelobe level, 45 degree of beam tilt angle in center frequency. Feed network designed by waveguide cooperated feed shows good performance of wideband and low loss.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.4 no.2
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• pp.24-33
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• 1993

In indoor radio systems, vehicular communication systems, and land mobile systems, a very important problem is that of maintaing stable communications at all locations. Therefore solutions for the indoor propagation problem are an important aspects of the mobile communication system. Leaky coaxial cables finding increasing use in communications systems involving mines, tunnels, railroads, and highways, and in new obstacle detection, or guided radar, schemes for ground transpor- tation and perimeter surveilance. In this paper a leaky coaxial cable having periodic slots in the outer conductor is described to obtain the propagation modes in the various environments. We use an essentric cylindrical model to develop the theory for surface-wave propagation on the cable. Numerical Results are also included for the propagation constants, field distribution and impedance as functions of various parameters. First, we derive the electromagnetic equation for leaky coaxial cable having periodic slots using mode-matching method and Floguet's theorem, and then find various modes, propagation constants, field distribution, etc.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.3
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• pp.209-214
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• 2017

A plane-wave incident upon asymmetric multi-layered dielectric grating as well as symmetric grating structure generates space harmonics. Selected space harmonics among those harmonics can undergo strong resonance scattering variations known as GMR(guided-mode resonance). In this paper, to clarify these effects, the field propagation and dispersion curve inside the grating region are analyzed by using a rigorous equivalent transmission-line theory(RETT) based on eigenvalue problem. The results show that, at the peak of a scattering resonance, the reflected mode is almost identical to a leaky wave that can be supported by the grating structure. Thus, it confirms to be occurred GMR effect associated with the free-resonant character of leaky waves at asymmetric multi-layered dielectric gratings. Quantitative simulation results illustrating the behavior of typical gratings are given, and the special case of normal incidence is discussed for TE and TM modes.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.22 no.5
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• pp.123-128
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• 2022

Applying rigorous modal transmission-line theory (MTLT), the properties of resonant diffraction gratings under conical light incidence is investigated. The mode vectors pertinent to resonant diffraction under conical mounting vary less with incident angle than those associated with diffraction gratings in classical mounting. Furthermore, as the evanescent diffracted waves drive the leaky modes responsible for the resonance effects, the conical mounting imbues diffraction gratings with larger angular tolerance than their classical counterparts. Based on these concepts, the angular-spectral and wavelength-spectral performance of resonant diffraction gratings in conical and classical mounts by numerical calculations with spectra found for conical incidence are quantified. These results will be useful in various applications demanding resonant diffraction gratings that are efficient and physically sparse.

• Journal of electromagnetic engineering and science
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• v.1 no.2
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• pp.161-165
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• 2001

The radiation characteristics of leaky wave emanated from finite strip-grating loaded dielectric coated coaxial waveguide with finite periodic thick slots are investigated theoretically. The rigorous integral equations are derived for the proposed structure using the courier transform, mode expansion, and sine series expansion of the electric current on metallic strips, and the simultaneous linear equations are obtained. The effects of finite strip-grating loading on a dielectric-coated coaxial waveguide with finite periodic thick slots are examined in terms of radiation characteristics.

• Korean Journal of Optics and Photonics
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• v.13 no.6
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• pp.473-478
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• 2002

Circular slab waveguides are conformally mapped into straight waveguides. In the outer cladding region with monotonically increasing index profile, modified Airy functions (MAF) of traveling-wave form are introduced to express the leaky mode. Field distributions and losses calculated by the proposed method are compared with those obtained by the WKB (Wentzel-Kramers-Brillouin) method. Detailed numerical examples are presented and compared with the conventional WKB methods, demonstrating our method not only allows a converging field at turning points but also guarantees fine accuracy.