• Journal of Convergence for Information Technology
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• v.7 no.5
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• pp.83-88
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• 2017

This paper describes the azimuth accuracy test of phase comparison direction finding method using F-16 fighter scale-down model. When the antennas are placed on the bottom of a fighter, reflection signals caused by an aircraft structure arises and an azimuth error occurs. In this research, the F-16 fighter scale-down model was made to 5:1, and five antennas were placed on the bottom of the model, then the radio waves of emitters were received by the antennas in the $0-360^{\circ}$ azimuth angles. The accuracy test was performed by numerically analyzing the phases of the radio waves received by the five antennas. The azimuth error of the phase comparison direction finding with scale-down model was measured to be less than $0.5^{\circ}$ when the signal noise ratio was larger then 0dB, and it could be very useful for the design of the phase comparison direction finding method of the fighter.

• Journal of Digital Convergence
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• v.11 no.1
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• pp.283-288
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• 2013

In this study, we introduce a 3D micro-cell simulator for radio wave propagation analysis in indoor environments. Previous studies treat only the path loss between the transmitter and receiver in 2D geometry. We provide the simulation results of indoor propagation prediction based on various ITU-R Recommendations. Simulation results described here indicate that the low and high frequency bands give quite different characteristics in presented indoor geometry. The propagation loss as a function of distance has two distinct regions. It is similar to that occurring in free space within 5-20m of the transmitter, however, increases significantly as the electromagnetic waves become obstructed by the walls at distances further away in the next region.

• The Journal of Korean Association of Computer Education
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• v.23 no.1
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• pp.77-90
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• 2020

The purpose of the study is to provide educational implications for more effective Problem-based learning(PBL) by investigating students' learning types based on their online learning behaviors. A total of 1,341 students participated in the study, and they engaged in a six-week-long PBL program run by K University. For the study, participants' online activity data were collected. From the data, a total of 48 variables that represent their various online learning behaviors were extracted. Based on the variables, hierarchical cluster analysis was conducted to analyze learning types. Also, the differences in learning characteristics and achievements were investigated by considering types of learning. As a result, the learning types in online PBL were classified as 'high-level participation (cluster 1)', 'medium-level participation (cluster 2)', and 'low-level participation (cluster 3)'. In addition, the achievement level was found to be highest in 'high-level participation (cluster 1)' and lowest in 'low-level participation (cluster 3)'. Based on the results, the implications for improving online PBL were suggested.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.7
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• pp.1536-1541
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• 2009

In this paper, we present a novel pulse train identification method for two step stagger pulse train. Generally radar uses a fixed pulse train, and it is easy for electronic warfare system to measure the pulse repeat interval(PRI) and identify the radar. But it is very difficult to measure the PRI of stagger pulse radar because the pulse interval is periodically changed. We suggest a novel method to measure the PRI and identify the radars using the second deviation of pulse train. This method is faster comparing with Histogram method. We have a good PRI measurement results for 2 step stagger signals.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.8
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• pp.1832-1838
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• 2009

In this paper, we present new signal de-interleaving method for the frequency agility radar in which the carrier frequency is changed irregularly. Generally radar use a fixed carrier frequency, and it is easy for electronic warfare system to de-interleave the radar signal with respect to the frequency, pulse width(PW), and direction of signal arriving(DOA). In frequency agility radar, it is difficult to de-interleave the radar signals according to the carrier frequency because the frequency is changed irregularly. We suggest a good de-interleaving method to identify the frequency agility radar signals in comparison with PRI's of radars. First we calculate pulse repeat Interval(PRI) of radar in linked-list and queue structure and de-interleave the radar signals with PRI, PW, and DOA, then identify the frequency agility radar. When we use the proposed algorism to the frequency agility radar, we have a good de-interleaving results with electronic warfare systems.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.11
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• pp.5208-5213
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• 2011

In this paper, we proposed a new direction finding(DF) technology using TDOA(time-difference of arrival) and PDOA(phase difference of arriving signal) method. The proposed technology has a good DF accuracy without DF ambiguity. TDOA or PDOA technology is used to the most of intelligence systems in 21 century. The principle of TDOA is to receive a signal with two parallel antennas, measure the time difference of arrival signal, and converse the time difference to the direction of incident signal. Those technology make a DF system small size but the DF accuracy is low into short antenna installation distance. The principle of PDOA is similar to TDOA except measuring the phase difference of arrival signal, These technology get a good DF accuracy in short antenna installation distance but have a DF ambiguity. The proposed DF method is simulated into DF system operation environment with noise, and has a good DF accuracy.

• Journal of Convergence for Information Technology
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• v.7 no.2
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• pp.37-42
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• 2017

In order to estimate chaff RCS, we suggest here a novel method using the probability distribution. Normally, a chaff is assumed that it is a thin dipole antenna and the RCS can be calculated by the scattering wave theory. Most of the theoretical methods presented were mainly focusing on a single chaff cloud. In this paper, the RCS calculation was done for two or more chaff clouds and the changes of RCS with azimuth angle were observed. Matlab was used for presenting the probability distribution of chaff clouds and RCS calculation. A more accurate RCS estimation method is suggested by estimating the number of chaffs except the blocked elements.

• Journal of Convergence for Information Technology
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• v.11 no.8
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• pp.23-28
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• 2021

In this paper, we analyze the tracking errors of monopulse radar according to the JSR of retrodirective cross-eye and radar skin return signals. The cross-eye jammer gain(G_c) is used to calculate the radar tracking errors, and the relationship between the jammer gain and the JSR is represented mathematically. We analyze the radar tracking errors by varying the tracking angle and JSR. Analysis results of the phase difference(ϕ) and amplitude ratio(a) between the two jammer signals and the changing JSR show that the closer the phase difference of the two jammer signals is to 180, the greater the tracking error and it shows that if the JSR is above 20dB, the tracking errors no longer increase. This work presents an effective utilization of retrodirective cross-eye jammers through various tracking error analyses based on the JSR, tracking angles, two-jammer phase differences and amplitude ratios of two-jammer signals.

• Journal of Convergence for Information Technology
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• v.9 no.5
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• pp.125-129
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• 2019

This paper describes the jamming effect of phase-coded pulse compression(PCPC) radar. Barker code radar, a typical PCPC radar, separates transmission pulses into 13 or 31 small pulses and phase modulates and transmits each pulse signal to increase radar detection efficiency and reduce the influence of jamming. Generally, when the radar is subjected to jamming, the detection distance becomes shorter and the detection error rate becomes higher. In the case of noise jamming or carrier jamming on the PCPC radar, the jamming effect is very small for no phase-coded convergence. However, the jamming effect is large in the case of synchronous jamming using the pulse-coded signal as a jamming signal with DRFM. It can be seen that the jamming effect increases when the storage time of the pulse-coded signal is prolonged. This study is considered to be useful for PCPC radar and EW jamming system design.

• Journal of Convergence for Information Technology
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• v.12 no.4
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• pp.9-13
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• 2022

In this paper, the tracking error of monopulse radar caused by cross-eye jamming using terrain bounce is analyzed. Cross-eye jamming is a method of generating an error in a radar tracking system by simultaneously transmitting two signals with different phases and amplitudes. When the monopulse radar receives the cross-eye jamming signal generated by the terrain bounce, a tracking error occurs in the elevation direction. In the presence of multipath, this signal is a combination of the direct target return and a return seemingly emanating from the target image beneath the terrain surface. Terrain bounce jamming has the advantage of using a single jammer, but the space affecting the jamming is limited by the terrain reflection angle and the degree of scattering of the terrain. This study can be usefully used to protect ships from low-altitude missiles or aircraft in the sea.