• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.3
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• pp.519-526
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• 2016

As marine accidents happen frequently, it is required to establish a marine traffic monitoring system, which is designed to improve the safety and efficiency of navigation in VTS (Vessel Traffic Service). For this aim, recently, X-band marine radar is used for extracting the sea surface information and, it is necessary to retrieve wave information correctly and provide for the safe and efficient movement of vessel traffic within the VTS area. In this paper, three different current estimation algorithms including the classical least-squares (LS) fitting, a modified iterative least-square fitting routine and a normalized scalar product of variable current velocities are compared with buoy data and then, the iterative least-square method is modified to estimate wave information by improving the initial current velocity. Through several simulations with radar signals, it is shown that the proposed method is effective in retrieving the wave information compared to the conventional methods.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.6
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• pp.504-511
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• 2016

In this paper, the method is proposed that the equivalent result can be obtained by compensating the variation of gain and phase in the comparison with the result of near-field measurement which is obtained in the steady state, although the gain and phase variation of rx-channels occurred in the near-field rx-measurement of digital active phased array antenna. The proposed concept has the time section for monitoring the state of the rx-channels through the calibration path in the measurement timeline, and is the method for compensating the variation of state. For validating the proposed method, the fabricated X-band digital active phased array antenna and the planar near-field measurement facility is utilized. The proposed method is validated in the comparison with the compensated pattern which the unstable state of rx-channels is calibrated and the reference pattern obtained under the steady state of the rx-channels.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.22 no.6
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• pp.31-36
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• 2022

In this paper, we present the design, manufacture and test results of Backend unit for SAR(Synthetic Aperture Radar) that can be applied on a small satellite. The Backend unit for SAR was designed with a control/storage board, TRX(transmission and receiving) board and a power supply board as a single unit in consideration of the applying of a small satellite. The control/storage board uses RFSoC to generate wideband chirp signal, generate operating timings, and perform control and calculations for SAR operation. The TRX board is designed to convert the wideband chirp signal generated by the control/storage board to the operating frequency of X-band by up-converting the frequency. Since small size, light weight, and low cost are important consideration for small satellite, MIL/Industrial grade components were appropriately applied and the at the same time it was designed to ensure mission life through the radiation test, analysis and space environment tests.

• Journal of electromagnetic engineering and science
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• v.17 no.3
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• pp.153-158
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• 2017

This work reports on the effect of plasma area on the frequency characteristics of the monostatic radar cross section (RCS) of a square metallic plate. A dielectric barrier discharge (DBD) plasma actuator consisting of 10 rings is proposed. The actuator is fabricated in three different configurations such that only three inner rings, seven inner rings, and all rings can be biased. By applying an 18-kV bias at 1 kHz, the three types of DBD actuators generate plasma with a total area of 16.96, 36.74, and $53.69cm^2$, respectively, in a ring or circular form. The experimental results reveal that when the DBD actuator is placed in front of a $20mm{\times}20cm$ conducting plate, the monostatic RCS is reduced by as much as 18.5 dB in the range of 9.41-11.65 GHz. Furthermore, by generating the plasma and changing the area, the frequency of maximum reduction in the monostatic RCS of the plate can be controlled. The frequency is reduced by nearly 20% in the X band when all rings are biased. Finally, an electromagnetic model of the plasma is obtained by comparing the experimental and full-wave simulated results.

• Composites Research
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• v.29 no.6
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• pp.336-341
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• 2016

This paper conducted the study on the electromagnetic and mechanical applicability of CNT-coated glass fiber for wind blades. Large-size wind blade has the serious pending problems to meet the target, such as interfering radar signals, increasing weights, and increasing repair costs. In this paper, we are suggesting the CNT-coated glass fiber in order to overcome these problems. First, the CNTs were strongly coated on the surfaces of glass fiber by suggested coating process, and the CNT-coated glass fiber/epoxy composites were fabricated by Va-RTM process. We designed and fabricated a radar absorbing structure using the CNT-coated glass fiber, which showed over 90% radar absorbing performance between 8.3 and 12.1 GHz frequency. In addition, we confirmed the improvement of mechanical properties on the strength and modulus of tensile, compressive, and in-plane shear.

• Journal of Korean Society for Quality Management
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• v.47 no.3
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• pp.437-451
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• 2019

Purpose: The purpose of this study is to improve the quality of the PGM system by improving the structure and production process of slip-ring rotary joint for radar. Methods: The improvement measures for each cause are established through failure analysis of broken items. Specifically, changing in the housing to improve the heating system. Changing the transportation method to prevent damage to equipment during transport. Changing work process of the attenuator ring to prevent damage. etc. Results: The results of this study are as follows; improving the heating system reduces heat generated by the attenuator by about 7 degrees and obtain additional temperature margins. Reduction of defect rate because of adding X-band rotary joint run-out measurement test, ESS of slip-ring rotary joint and Transportation improvement(reinforced flight boxes, tube protection, etc). Getting stable VSWR values by improving work process of attenuator overheating due to a bad bonding process. Conclusion: Through this study, improvements were made to slip-ring rotary joint that failed repeatedly for various reasons. As a result of the application of the improvements, the same fault does not occur until now, so we can see that the quality of PGM has improved.

• Korean Journal of Remote Sensing
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• v.35 no.6_4
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• pp.1373-1389
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• 2019

KOMPSAT-5 is the first satellite in Korea equipped with X-band Synthetic Aperture Radar (SAR) instrument and has been operated since August 2013. KOMPSAT-5 is used to monitor the global environment according to its observation purpose and the availability of KOMPSAT-5 is also highlighted as the need of high resolution wind data for investigating the coastal region. However, the previous study for the validation of wind derived from KOMPSAT-5 showed that the accuracy is lower than that of other SAR satellites. Therefore, in this study, we developed the correction equation of normalized radar cross section (NRCS or backscattering coefficient) for improvement of wind from the KOMPSAT-5 and validated the effect of the equation using the in-situ measurement of ocean buoys. Theoretical estimated NRCS and observed NRCS from KOMPSAT-5 showed linear relationship with incidence angle. Before applying the correction equation, the accuracy of the estimated wind speed showed the relatively high root-mean-square errors (RMSE) of 2.89 m s^-1 and bias of -0.55 m s^-1. Such high errors were significantly reduced to the RMSE of 1.60 m s^-1 and bias of -0.38 m s^-1 after applying the correction equation. The improvement effect of the correction equation showed dependency relying on the range of incidence angle.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.520-520
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• 2015

본 연구는 현재 한국건설기술연구원에서 운영중인 수문레이더의 관측자료를 사용자가 쉽게 파악할수 있도록 모바일 정보제공 시스템을 구축하는데 있다. 모바일 앱 개발 방식은 대체적으로 모바일 웹, 하이브리드 앱, 네이티브 앱 크게 3가지로 구분할 수 있다. 모바일 웹 방식은 웹 시스템을 모바일 사이즈에 맞게 개발하여 브라우저를 지원하는 모든 기기에서 사용할 수 있고 유지보수가 편한 장점이 있다. 그러나 디바이스의 리소스 접근이 힘들고 네트워크 사용이 힘든 경우 따로 기능을 사용 할 수 없다. 네이티브 앱 방식은 디바이스의 리소스 사용이 용이하고 네트워크 사용이 힘든 경우 기능 사용이 가능하나 OS별 개발과 버전별로 기능 구현에 따른 제약이 있고 유지보수가 힘들고 개발 비용이 많이 든다. 하이브리드 앱은 네이티브 앱과 웹 앱의 장점을 합친 형태로 핵심 기능들은 네이티브 앱으로 구현하고 지속적인 업데이트가 필요한 부분은 웹을 통해 관리하도록 구현한다. 때문에 디바이스 리소스 사용이 용이하고 네트워크 사용이 힘든 경우에도 기능 사용이 가능하다. 또 유지보수가 편하고 다양한 기기에 적용할 수 있는 장점이 있어 본 모바일 시스템은 하이브리드 앱 방식을 적용하여 개발하였다. 모바일서는 레이더 관측자료인 반사도와, 현재 강수량 및 10분 강우량, 1시간 강수량을 표출하였다.

• Journal of Cadastre & Land InformatiX
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• v.47 no.2
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• pp.79-90
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• 2017

Urban environment represent one of the most dynamic regions on earth. As in other countries, forests, green areas, agricultural lands are rapidly changing into residential or industrial areas in South Korea. Monitoring such rapid changes in land use requires rapid data acquisition, and satellite imagery can be an effective method to this demand. In general, SAR(Synthetic Aperture Radar) satellites acquire images with an active system, so the brightness of the image is determined by the surface roughness. Therefore, the water areas appears dark due to low reflection intensity, In the residential area where the artificial structures are distributed, the brightness value is higher than other areas due to the strong reflection intensity. If we use these characteristics of SAR images, settlement areas can be extracted efficiently. In this study, extraction of settlement areas was performed using TerraSAR-X of German high-resolution X-band SAR satellite and KOMPSAT-5 of South Korea, and object-oriented image classification method using the image segmentation technique is applied for extraction. In addition, to improve the accuracy of image segmentation, the speckle divergence was first calculated to adjust the reflection intensity of settlement areas. In order to evaluate the accuracy of the two satellite images, settlement areas are classified by applying a pixel-based K-means image classification method. As a result, in the case of TerraSAR-X, the accuracy of the object-oriented image classification technique was 88.5%, that of the pixel-based image classification was 75.9%, and that of KOMPSAT-5 was 87.3% and 74.4%, respectively.

• Journal of Advanced Navigation Technology
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• v.8 no.1
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• pp.57-65
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• 2004

In this paper, keeping pace with light weight, pocket-size, lower-price, we design VCO(Voltage Controlled Oscillator) X/Ku band for using at public RD(Radar Detector) to apply to controlled voltage on base in transistor which used as a oscillator, without using varactor diode in part of VCO tuner. As a result of simulation, we conclude VCO could be have 110 MHz by controlled voltage 4.25 V to 4.80 V and show its output 9.63 dBm at operating frequency, 11.46 GHz, and its phase noise -107.2 dBc at 1 MHz offset frequency. So it turned out suitable performance for commercial use.