• Journal of the Institute of Electronics and Information Engineers
• /
• v.53 no.6
• /
• pp.21-28
• /
• 2016

This paper presents a cooperative transmission scheme for underwater acoustic sensor networks to improve packet transmission rate and reduce energy consumption. Source node transmits duplicated information relayed by distributed antennas called a virtual antenna array. Destination node combines that information to reduce packet error rate. The suggested cooperative scheme enhances the reliability by providing high diversity gains through intermediate relay nodes to overcome the distinct characteristics of the underwater channel, such as high transmission loss, propagation delay, and ambient noises. It is suggested that the algorithm select destinations and potential relays from a set of neighboring nodes that utilize distance cost, the residual energy of each node and local measurement of the channel conditions into calculation. Simulation results show that the proposed scheme reduces average energy consumption, response time, and increases packet delivery ratio compared with the SPF(Shortest Path First) and non-cooperative scheme using OPNET Moduler.

• Journal of Astronomy and Space Sciences
• /
• v.37 no.2
• /
• pp.143-156
• /
• 2020

Korea Polar Research Institute (KOPRI) installed an ionospheric sounding radar system called Vertical Incidence Pulsed Ionospheric Radar (VIPIR) at Jang Bogo Station (JBS) in 2015 in order to routinely monitor the state of the ionosphere in the auroral oval and polar cap regions. Since 2017, after two-year test operation, it has been continuously operated to produce various ionospheric parameters. In this article, we will introduce the characteristics of the JBS-VIPIR observations and possible applications of the data for the study on the polar ionosphere. The JBS-VIPIR utilizes a log periodic transmit antenna that transmits 0.5-25 MHz radio waves, and a receiving array of 8 dipole antennas. It is operated in the Dynasonde B-mode pulse scheme and utilizes the 3-D inversion program, called NeXtYZ, for the data acquisition and processing, instead of the conventional 1-D inversion procedure as used in the most of digisonde observations. The JBS-VIPIR outputs include the height profiles of the electron density, ionospheric tilts, and ion drifts with a 2-minute temporal resolution in the bottomside ionosphere. With these observations, possible research applications will be briefly described in combination with other observations for the aurora, the neutral atmosphere and the magnetosphere simultaneously conducted at JBS.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.15 no.11
• /
• pp.1108-1115
• /
• 2004

A new type of a Rotman lens is presented in this paper fur millimeter-wave applications, such as collision avoidance radar. A dielectric slab Rotman lens is proposed to reduce the conductor loss and to create an appropriate farm for favorable implementation at millimeter-wave frequency. The proposed lens consists of a dielectric slab and slot lines whereas the conventional lenses are constructed with parallel conducting plates. The dielectric slab Rotman lens excited in TE$\_$0/ mode shows a high degree of confinement for the fields, low dispersion, and has an appropriate feed structure. A prototype lens has been designed and fabricated with 9 beam ports and 9 array ports together with 9 tapered slot antennas. This lens has been tested in the range from 10 GHz to 15 GHz and the measured beam widths are about 15$^{\circ}$ at 13 GHz. The measurements also show low mutual coupling between beam ports and an efficiency of about 34.6 %. The overall performance is comparable to that of conventional Rotman lenses even though the prototype was tested at lower than desired frequencies in the microwave frequency range due to our limited resources for fabrications and measurements. It is expected that at millimeter-wave frequency the dielectric slab Rotman lens will have lower conductor loss and lower mutual coupling than conventional Rotman lenses.an lenses.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.20 no.7
• /
• pp.648-656
• /
• 2009

We perform an analysis of the characteristics of the time-reversal pulse in Rayleigh or Ricean fading channel environments. We verify it by using Monte Carlo simulation. In a time-reversal system, each antenna in the time-reversal array receives signals from the transmitter and reverse the received signal in the time axis and then resend it to the original transmitter. We assume that the channel characteristics varies very slowly and the spatial separation between the antennas is not large. Hence the signals received by each antenna are correlated. In this paper, the effect of the correlation on the time-reversed pulse is examined, which includes the spatial properties of the time-reversal pulse such as the focus size, and spatial power distribution.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.28 no.7A
• /
• pp.537-546
• /
• 2003

This paper proposes an aperture coupled circular polarized patch antenna operating at ISM band(5GHz). For improving the characteristic and performance of broadband and circular polarization at single circular polarized patch antenna. We designed and analyzed the sequentially rotated arrayed(SRA) using phase delay of 0$^{\circ}$, 90$^{\circ}$, 180$^{\circ}$, 270$^{\circ}$and 0$^{\circ}$, 45$^{\circ}$, 90$^{\circ}$, 135$^{\circ}$. Experimental result, the SRA antenna using phase delay of 90$^{\circ}$and 45$^{\circ}$are improved at the wideband and axial ratio. Also, the SRA antenna using phase delay of 45$^{\circ}$verified that it is better bandwidth and axial ratio than the SRA antenna using phase delay of 90$^{\circ}$.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.5A
• /
• pp.433-440
• /
• 2007

In this paper, we have proposed WiBro receiver structure employing joint adaptive antenna scheme at the base station (BS) and the mobile station (MS) and evaluated its performance. In WiBro system, the joint use of transmit beamforming at BS and receive beamforming at MS can improve the SINR significantly and increase the capacity compared to the conventional system. Moreover, power allocation level can be decreased because channel variation can be reduced by using the jointly updated weight. However, it needsthe calculation of the antenna weights in every subcarrier for performance improvement. This could imply an enormous computational burden. However, the computational complexity can be reduced significantly by using the same set of the antenna weights for the adjacent subcarriers instead of calculating antenna weights for every subcarrier. We have analyzed the impact of subcarrier grouping for weight calculation on the system performance.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.6 no.3
• /
• pp.95-100
• /
• 2007

In this paper, a twice folded TEM horn antenna for 70 kV impulse high power system is proposed. The length reduction of 50 % is achieved by folding a conventional TEM horn antenna twice. The array elements are fed by the stripline power divider using the Chebyshev transformer. The power divider feeds four TEM horn antenna elements with an in-phased uniform power, and it covers a wide bandwidth ($150\;MHz\;{\sim}\;768\;MHz$, VSWR<2.0). Considering the air breakdown at peak 70 kV impulse, the proposed antenna maintains the 25 mm gaps between conducting plates. The dimension of the twice folded horn antenna is $1730\;{\times}\;1600\;{\times}\;300$ (mm3), and the operating frequency is from 152 MHz to 750 MHz under 10 dB return loss. The peak gains are measured from 6.77 dBi to 10.70 dBi at $400\;MHz\;{\sim}\;750\;MHz$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.9 no.6
• /
• pp.813-823
• /
• 1998

This paper analyzed the circularly polarized conformal microstrip patch antennal using the unsplit anisotropic perfectly matched layer(UAPML) method. Also, this paper are treated effectively the edge and corner parts on the 3 dimensional UAPML. Especially, to analyze microstrip patch antennas with the coaxial feeder line, it was applied to mixed the UAPML with Mur's first order absorbing boundary condition. Therefore this paper suggest the new the method to mix the UAPML with Mur's first order absorbing boundary condition. The results show the time responses of electromagnetics $E_z$ and $H\chi'$, input impedances of coaxial cable and radiation patterns of strip parchs on the single and the array patchs with central frequencies 1.575 GHz, 1.778 GHz and 4.8 GHz in L-band and C-band for mobile communication. The results of this paper shows that its results was compared the Mur's first order abc and mixed the second order dispersion boundary condition(SDBC) with the Mur's first order absorbing boundary condition. In accordance with, the validity of the method is confirmed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.29 no.4
• /
• pp.320-323
• /
• 2018

Herein, an ultrawideband spinning direction finding (DF) antenna was designed and fabricated for airborne applications. The proposed antenna is designed by dividing the low-band (UHF - L band) and high-band (S - Ka band) antennas to cover the ultrawideband frequency range (UHF - Ka band). For the high-band antenna, an LPDA antenna fed offset-parabolic-reflector antenna is applied. In the low-band antenna, two LPDA antenna elements are arrayed in front of the reflector of the high-band antenna without increasing to the full antenna size. The low- and high-band gains of the fabricated antenna were measured as 8.76 dBi and 24.55 dBi on average, respectively. The antenna was fabricated with the dimensions of 437 mm in diameter and 358 mm in height. Consequently, we confirmed that the designed antenna is appropriate for the spinning DF antenna in terms of the affordable size for installing on an airplane, as well as the high gain and narrow beamwidth.

• Journal of Advanced Navigation Technology
• /
• v.21 no.5
• /
• pp.466-471
• /
• 2017

SOTM is a device for the satellite communication on the move. Many studies are conducted on microstrip, waveguide and array antenna for the low profile of the SOTM's antenna. But those antennas have a problem that is difficult to adjust the polarization, and for that reason we have studied the parabolic antenna structure. The general form of parabolic reflector structure is circular, but we used cut-off shape reflector by cutting the upper and lower reflector for low profile antenna. Accordingly, this results in the decrease of reflector area which causes reduced gain and G/T ratio. In order to solve this problem, we have transformed and designed the sub reflector for improving the efficiency and gain of the cut- off shape parabolic antenna.