• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.4
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• pp.499-505
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• 1998

This paper presents the method for an estimation of discharge current waveshapes in short gap discharge by a radiated electromagnetic field. The method of currentwaveform estimation described is using the one antenna method(single field method) with a measured electric or magnetic fields at given field point by a time domain antenna. In order to verify the availability of the estimated theory, the discharge current waveshape estimation was performed by one antenna method using the measured electric fields of Wilson & Ma and compared with experiments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.10
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• pp.2703-2709
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• 1996

This paper proposes an exact numerical method for analyzing a dipole antenna attached on a dielectric slab. A Green's function for an infinitesimal current filament on a dielectric slab is derived and a field integral equation is formulated using a boundary condition. The moment Method is used to solve the field integral equation to otain current distribution on the antenna. Since an asymptotic function is used to compute the impedance matrix elements, the computataion time is significantly reduced. Using the computed current distributions, the input impedances, the resonance lengths and the resonant resistances of the antennas for various values of the thichnessandthe dielectric constant of the slab are obtained. It was found that the resonant length and the resonant resistance are decrease monotonically as the dielectric constant increases, however, those are changed up-and-down as the substrate thickness increases.

• Journal of Biomedical Engineering Research
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• v.18 no.3
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• pp.261-266
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• 1997

Nonevasive multifrequency microwave radiometry using coaxial waveguide antenna has been investigated for a homogeneous and four layer human body model. The coupling between coaxial waveguide antenna and a biological object was analyzed by use of the finite-difference time-domain(FDTD) method to obtain the absorbed power patterns in the media. The object studied in this paper was a homogeneous and four-layered lossy medium. The specific absorption rates(SAR) distribution which was corresponding to the temperature distribution was calculated in each region by use of the steady-state response in FDTD method. The SAR pattern of 1.2GHz was compared with that of 1.8GHz.

• Proceedings of the KIEE Conference
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• 2003.11c
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• pp.689-692
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• 2003

In this paper, we propose an adaptive beamforming algorithm for array antenna. The proposed beamforming algorithm, based on Block LMS (Block - Least Mean Squares) algorithm, has a variable step size from coefficient update. This method shows some advantages that the convergence speed is fast and the calculation time can reduced using a block LMS algorithm from frequency domain. As the adaptive parameter approaches a stationary state, it could reduce the number of filter coefficient update with the help of various step size. In this paper we compared the efficiency of the proposed algorithm with a standard LMS algorithm which is a representative method of adaptive beamforming.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.1
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• pp.98-105
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• 2013

This paper presents a finite-difference time-domain(FDTD) simulation and a data processing technique for radar sensing of the internal structure of a wall using an ultra-wide band antenna. We first designed an ultra-wide band anti-podal vivaldi antenna with a frequency range of 0.3~7 GHz which is chosen to be relatively low after considering the characteristics of wave attenuation, wall penetration, and range resolution. In this study the two-dimensional FDTD technique was used to simulate a wall-penetration-radar experiment under practical conditions. The next, the measured radiation pattern of the practical antenna is considered as an equivalent source in the FDTD simulation, and the reflection data of a concrete wall and targets are obtained by using the simulation. Then, a data processing technique has been applied to the FDTD reflection data to get a radar image for remote sensing of the internal structure of the wall. We compared the two different source excitations in the FDTD simulation; (1) commonly-used isotropic point sources and (2) polynomial curve fitting sources of the measured radiation pattern. As a result, when we apply the measured antenna pattern into the FDTD simulation, we could obtain about 2.5 dB higher signal to noise level than using a plane wave incidence with isotropic sources.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.2
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• pp.206-216
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• 2000

In this paper, the linear tapered slot(LTS) antenna and linear constant tapered slot(LCTS) antenna are optimized for millimeter-wave antenna by the finite difference time domain(FDTD) method and then fabricated and measured. The microstrip-to-slot transition is proposed with the widen $\lambda$/4 open stub as feeder for wide bandwidth of 16.5GHz($VSWR\leq2$). The results of the calculation and measurement, the bandwidth of LTS antanna is 8.3GHz(26.47%) and 7.1792GHz(22.4%) respectively. Also, the bandwidth of LCTS antenna is 8.1GHz(26.47%) and 6.3243GHz(20.43%) respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.4
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• pp.619-626
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• 2000

The electromagnetic fields of the corrugated annular feed-horn antenna have been analyzed exactly by using the finite-difference time-domain (FDTD) technique. The radiation pattern and return loss characteristics of the antenna were obtained as a function of the impedance of feeding coaxial line at 11.8GHz. The return loss was determined to be less than -25dB at 30$\Omega$. It was confirmed that the phase error is less compared to that of the antenna without corrugation, but the directivity of the radiation pattern needs to be improved.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.5
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• pp.251-258
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• 2002

In this paper, the dipole-fed planar array antenna applied Yagi-Uda antenna away theory to microstrip antenna is designed and fabricated at X-band. The design procedure of the dipole-fed planar array antenna with the wide bandwidth is presented to be easily practiced to a wireless communication system. The radiation pattern, return loss and bandwidth of the antenna are improved by the finite differential time domain(FDTD) numerical method. The propriety of analysis of planar dipole antenna is proved from the measured data. From the measured results, the antenna maximum gain is 4.9dBi at center frequency of 10GHz and frequency bandwidth is about 40%. Front-to-back ratio is 16dB, and half-power beam-width of E-plane and H-plane are 117$^{\circ}$and 156$^{\circ}$, respectively. When VSWR of antenna is less than 2, the measured results are agreed well with the theoretical values in the frequency range from 7.4GHz to 11.88GHz.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.1
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• pp.12-22
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• 2016

Convenience and safety are the key words for the automotive driving and various sensor technologies have been studied for enhanced perception of driving environments. In frequency modulated continuous wave (FMCW) radar systems, single antenna is enough for range and velocity detection of multiple targets. Multiple array antenna is needed for estimating direction of arrival(DoA). Using DoA estimation algorithm in time domain as in the conventional systems, it is difficult to distinguish vehicles lie in the same angle. In order to facilitate the enhanced angle estimation, DoA estimation algorithm is applied in frequency domain. In this paper, the method for applying multiple signal classification(MUSIC) algorithm in frequency domain is suggested and the performance is analyzed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.7
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• pp.1459-1467
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• 1997

The current on the thin planar structure as an element of the transversely fed electromagnetically coupled(EMC) microstrip dipole array antenna is obtained by using the integral forms of the finite difference time domain(FDTD) method. This method was applied to calculating the optimum current distribution (Doplh-Tchebyscheff distribution) of each dipole element on the feed line as a function of their offset positions for the narrow main beam width and the side beam level below -20 dB. The current on each dipole substitutes for the electric and magnetic current densities on the virtual surface of the FDTD calculation to express the far field intensity, the calculation time and the computer memeory can be reduced to about 80% and 1.3 Mbyte, respectively. The calculated radiation patterns are compared to the measured values and these are in good agreement.