• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.6
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• pp.437-445
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• 2010

There is increasing interest, on the global basis, in the operation of ocean surface radars for measurement of coastal sea surface conditions to support environmental, oceanographic, meteorological, climatological, maritime and disaster mitigation operations. In south Korea, ocean surface radars are operating to monitoring oil spill, outflow from dike or preventing from safety-accidents in the 6 regions (16 radial sites) by main frequency about 13, 25 and 42 MHz until the present. However, that ocean surface radars have been operated on an experimental spectrum basis. In the results of 3~50 MHz band domestic analysis to improve the regulatory status of the spectrum used by oceanographic radars, it was demonstrated that sufficient frequency bands are available for oceanographic radars on the frequency band above 20 MHz. It is difficult to deploy and operate oceanographic radars in the sub-bands below 20 MHz except for 13 MHz band. For using HF ocean surface radars one should understand the spectrum environment in Korea and should prepare a suitable operating system and data processing techniques.

• ETRI Journal
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• v.29 no.6
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• pp.832-834
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• 2007

This letter presents a reconfigurable ground-slotted patch antenna using a PIN diode connection in slots to achieve dual-frequency operation. Slots in the ground plane increase the electrical length and thereby reduce antenna size by 53%. By controlling PIN diode conduction, we achieved band hopping while still satisfying the bandwidth requirements for K-PCS and WiBro bands.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2000.11a
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• pp.231-234
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• 2000

The corona in oil, the surface discharge in oil, the void discharge which could be in a transformer were imitated by using three electrodes with different shapes and the frequency bands of each ultrasonic signal were measured. After emitting artificial noises toward the transformer, only ultrasonic signals were extracted by frequency filtering, from the ultrasonic signals with noises at partial discharge. As a result, it was confirmed that the ultrasonic signals due to the corona in oil, the surface discharge in oil, the void discharge could be distinguished from the noises.

• Journal of Industrial Technology
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• v.22 no.B
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• pp.169-173
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• 2002

In this paper, we discussed an effective VDSL frequency plan for symmetric 10MDSL service. The frequency plan 998 and plan 997 for asymmetric VDSL services have been not optimally designed for 10MDSL services. To obtain the reaches and data rates of 10MDSL, we proposed two frequency allocation schemes : Static method and dynamic method. We can select frequency bands with their fixed boundaries in static method while with their variable boundaries in dynamic method. To show the effectiveness of our proposed methods, we performed some simulations about plan 997 and plan 998, new static method, and new dynamic method. According to the simulation results, the proposed dynamic method can provide the best data rates and reaches for 10 Mbps symmetric VDSL services.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.7 no.4
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• pp.279-287
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• 1996

Frequency occupancy data can provide information on both the actual ratio of usage of individual frequency channels and the average ratio of usage of these frequency bands so that the reserved capacity of the spectrum can be estimated. Such an estimate can be used for the planning of additional spectrum allocations and as a means of assessing the impact of new technologies on spectrum usage. In this paper, we introduce about the frequency occu- pancy measurement system that is developed in Korea. And, we introduce Frequency Occupancy Ratio with a time period and with a area zone by using radio monitoing measurement datas.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2006.07a
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• pp.376-376
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• 2006

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.5
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• pp.444-449
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• 2009

This paper presents the design of a dual band branch line hybrid coupler(BLHC) with different power division ratios at two bands. In the proposed design, transmission lines of the BLHC are transformed to $\pi$-type equivalent circuits which represent different impedances and $\lambda/4$ electrical length at two frequency bands. In order to verify the proposed method, a dual band coupler with different power division ratios is designed for 0.9 GHz and 2 GHz applications. The desired power division ratios are 1:1 and 1:3 at the two operating frequency bands. The measured results show excellent performance with an insertion loss of less than 0.33 dB, a return loss of less than -18.07 dB, and good isolation characteristics.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.12
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• pp.1314-1317
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• 2014

In this letter, we designed monopole microstrip antenna for WLAN / WiMAX system. The monopole antenna is designed by FR-4 substrate with size is $30mm{\times}40mm$. The proposed antenna is based on a planar monopole design which cover WLAN and WiMAX frequency bands. To obtainthe optimized parameters, we used the simulator, CST's Microwave Studio Program and found the parameters that greatly effect antenna characteristics. Using the obtained parameters, the antenna is designed. Thus the proposed antenna satisfied the -10 dB impedance bandwidth requirement while simultaneously covering the WLAN and WiMAX bands. And characteristics of gain and radiation patterns are obtained for WLAN/WiMAX frequency bands.

• The KIPS Transactions:PartB
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• v.11B no.3
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• pp.289-296
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• 2004

General watermarking techniques tend not to consider intrinsic characteristics of image, so that watermarks are embeded to entire images. In this paper, we present a watermarking algorithm based on wavelet domain, and the watermark is embedded into large coefficients in region of interest(ROI) being based on principle of multi-threshold watermark coding(MTWC) for robust watermark insertion. We try to accomplish both image duality and robustness using human visual system(HVS). The watermarks are embedded in middle frequency bands because the distortion degree of watermarked images appears to be less than lower frequency bands, and the embedded watermarks in the middle bands showed high extraction ratios after some distortion. The watermarks are consisted of pseudo random sequences and detected using Cox's similarity mesurement.

• Journal of IKEEE
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• v.22 no.2
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• pp.413-419
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• 2018

An UWB(Ultra Wide Band) antenna with band rejection characteristics is designed and implemented. A planar radiation patch with slot, parasitic elements on both sides of strip and ground plane on back side consist the proposed antenna. The slot in the radiation patch and parasitic elements contribute corresponding bands rejection characteristics. The slot contributes for WiMAX(World interoperability for Microwave Access, 3.30~3.70 GHz) band rejection and parasitic elements contribute for X-Band(7.25~8.395 GHz) rejection. Ansoft's HFSS(High Frequency Structure Simulator) was used to design the proposed antenna and performance simulations. Simulation result showed VSWR(Voltage Standing Wave Ratio) less than 2.0 for UWB band except for dual rejection bands of 3.30~3.86 GHz and 7.21~8.39 GHz. And VSWR measurement result for the implemented antenna shows less than 2.0 for 3.10~10.60 GHz band except dual rejection bands of 3.25~3.71 GHz and 7.25~8.46 GHz.