• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.6
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• pp.1092-1098
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• 2007

Since one decade, the detection of HFPD (High frequency Partial Discharge) has been proposed as one of the effective method for the diagnosis of the power component under service in power grids. As a tool for HFPD detection, Metal Foil sensor based on the embedded technology has been commercialized for mainly power cable due to its advantages. Recently, for the on-site noise discrimination, several PA (Pulse analysis) methods have been reported and the related software, such as Neural Network and Fuzzy, have been proposed to separate the PD (Partial Discharge) signals from the noises since their wave shapes are completely different from each other. On the other hand, the relevant fundamental investigation has not yet clearly made while it is reported that the effectiveness of the current methods based on PA is dependant on the types of sensors. Moreover, regarding the identification of the vital defects introducible into the Power Cable, the direct identification of the nature of defects from the PD signals through Metal Foil coupler has not yet been realized. As a trial for solving above shortcomings, different types of software have been proposed and employed without any convincing probability of identification. In this regards, our novel algorithm 'PA Map' based on the pulse analysis is suggested to identify directly the defects inside the power cable from the HFPD signals which is output of the HFCT and metal foil sensors. This method enables to discriminate the noise and then to make the data analysis related to the PD signals. For the purpose, the HFPD detection and PA (Pulse Analysis) system have been developed and then the effect of noise discrimination has been investigated by use of the artificial defects using real scale mockup. Throughout these works, our system is proved to be capable of separating the small void discharges among the very large noises such as big air corona and ground floating discharges at the on-site as well as of identifying the concerned defects.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.21 no.1
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• pp.148-156
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• 2007

This paper explains stocker system that is operated in the long distance and linear area. The power system of stocker system uses Contactless Power Supply(CPS) to reduce problems of particle generation. The circuit configuration of CPS is simplified than the conventional ones, and the prototype is designed for commercial product. To transfer output data(information) from crane(secondary vehicle system) of the CPS to Primary system optical modem and TMS320F243(DSP, TI) are used between primary and secondary. power system are used, and the output voltage is controlled by operating frequency modulation. This paper is applied to stocker system controlled as one to one communication between the moving part(secondary system) and fixed part(primary system) of crane using optical modem. The study makes one to multi communication between fixed part and moving part for the purpose of multi crane operation of stocker system and must be done in the future.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.11
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• pp.1047-1053
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• 2011

In this paper, we proposed an HF-band wireless power transfer system with adaptive frequency control circuit for efficiency enhancement in a short range. In general, a wireless power transfer system shows an impedance mismatching due to a reflected impedance, because a coupling coefficient is varied with respect to separation distance between two resonating loop antennas. The proposed method can compensate this impedance mismatching by varying input frequency of a voltage-controlled oscillator adaptively with respect to separation distance. Therefore, transmission efficiency is enhanced in a short distance, where large impedance mismatch occurs. The adaptive frequency circuit consists of a directional coupler, a detector, and a loop filter. In order to demonstrate the performance of the proposed system, a wireless power transfer system with adaptive frequency control circuits is designed and implemented, which has a pair of loop antennas with a dimension of 30${\times}$30 $cm^2$. From measured results, the proposed system shows enhanced efficiency performance than the case without adaptive frequency control.

• Korean Journal of Optics and Photonics
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• v.10 no.3
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• pp.226-232
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• 1999

We have investigated the output power performance of a continuous-wave chromium-doped YAG laser ($Cr^{4+}$:YAG laser), pumped by a Nd: YAG laser. With an output coupler of 1% transmission, we obtained as much as 400 mW of the average output power at 1.450 ${\mu}{\textrm}{m}$. The power slope efficiency of 8%, when the gain medium was cooled to 2$0^{\circ}C$. We tuned the wavelength of the $Cr^{4+}$:YAG laser, at pump power of 6 W, by using birefringent filter. As a result, lasing wavelength was tuned from 1.399 ${\mu}{\textrm}{m}$ to 1.532 ${\mu}{\textrm}{m}$, with the maximum output power of 340 mW at 1.4903 ${\mu}{\textrm}{m}$ and the linewidth was 0.21 nm.

• Journal of Advanced Navigation Technology
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• v.8 no.2
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• pp.184-190
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• 2004

A feedforward linear power amplifier (FLPA) has been developed for UHF-band RFID reader applications. The main and error amplifiers are composed of a 2 stage so that linearity of the FLPA can be improved. The FLPA has been implemented on an FR-4 substrate (Er=4.7 and thickness=0.8 mm) with 3-dB and 10-dB hybrid couplers for input/output power divider and combiner. For 2-tone measurement (input level=-11 dBm at $f_1$=915 MHz and $f_2$=916 MHz), the FLPA exhibits a -18.52 dBm of $IMD_3$, which indicates that $IMD_3$ cancellation with feedforward loop is more than 27 dB. From 890 to 960 MHz, 1-dB gain compression output power and power gain of the FLPA are higher than 30 dBm and 40 dB, respectively.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.1
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• pp.231-238
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• 2019

In this paper, we have studied how to improve the amplifiers efficiency by minimizing the combining loss when several unit power amplifiers are combined to obtain high output power. Specifically, we have developed Ka-band Spatial Combining Amplifier. The fabricated Spatial Combining Amplifier is a Ka-band 20W class SSPA, which uses a 5W class unit amplifier module 8EA designed using a GaN bare die. We also combined The unit amplifier module using 8-way spatial divider and combiner with a hybrid radial structure. The output combining loss of the fabricated spatial coupler is about 0.334dB, which is about 92.6% efficiency. In this paper, we developed a Spatial Combining Amplifier with a maximum saturation output of 10W and a power addition efficiency of over 15%. As a result, we achieved the maximum saturation output of 30W and the power addition efficiency of 19%.

• Korean Journal of Optics and Photonics
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• v.20 no.5
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• pp.266-271
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• 2009

We designed a thermo-optic switch based on a directional coupler with not only a high extinction ratio but also significantly low power consumption. The switch operates by using the thermo-optic effect of the polymer which the refractive index changes by heating the electrode. If the electrode is not powered (OFF), the input light will be coupled completely to the other waveguide. When the electrode is powered at a certain level (ON), input light launched into the input waveguide will remain in that waveguide due to the lower index adjusted in the other waveguide. The switch based on the directional coupler was designed using the generalized extinction ratio curve and the lateral shift of the input waveguide. The coupling length is 1,610 ${\mu}m$ and the extinction ratios are -28 and -30 dB for ON and OFF states, respectively. The electrode structures were optimized by thermal analysis. The transported heat into the waveguide is increased, as the electrode width (w) is increased and the center distance between the electrode and the waveguide (d) is decreased. Also, because the heat generated in the electrode affects the other waveguide, the temperature difference between two waveguides is varied as the given w and d. There are specific conditions which have the maximum of the temperature difference. That of the temperature difference is increased as the width and the temperature of the electrode are increased. Especially, when the switch is designed using the condition with the maximum of the temperature difference for switching, the temperature of the electrode can be decreased. We expect this condition will be the novel method for the reduction of the power consumption in a thermo-optic switch.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.2
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• pp.220-228
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• 2012

In this paper, we explained the design technique about Ka-band active limiter for protecting the receiver of a millimeter wave seeker. To implement low flat leakage power, we proposed the control circuit of active limiter to control limiter voltage with PRF(Pulse Repetition Frequency) signal and input power. This active limiter consisted of the conventional 2 stage passive limiter, a feedback circuit with a directional coupler, detector, non-inverting amplifier and over-current protection resistance. As the test result of the fabricated Ka-band limiter, it had 1 GHz bandwidth, 3.5 dB insertion loss at the small input power and -7.5 dBm flat leakage at the 4 W RF input power, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.10 s.113
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• pp.959-966
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• 2006

This paper proposes a new concept about dual band predistortion linear power amplifier(PD LPA) using diplexer for digital cellular ($f_o$=880 MHz) and IMT-2000($f_o$=2,140 MHz) base stations. The diplexer is composed of low pass filter having defected ground structure(BGS) microstrip line and high pass filter having high-Q lumped capacitors and distributed elements. The proposed predistorter adopts a reflection type intermodulation signal generator with 3 dB hybrid coupler for good reflection characteristic. for a forward link one carrier CDMA IS-95A 1FA and WCDMA 1FA signal, the proposed dual band PD LPA shows the adjacent channel leakage ratio(ACLR) improvement about 10 dB and 9.36 dB for digital cellular and IMT-2000 band, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.8
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• pp.709-716
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• 2016

In this paper, A duplexer module with temperature-insensitive electrical characteristics was proposed for remote wireless communication system. Duplexer modules are required to have performances of low insertion loss, high isolation between transmitted band and received band, harmonic suppression as well as high power durability in the system for transmitting guided information to missile flying a free space on the ground. The proposed duplexer module are consist of transmission bandpass filter and receiving bandpass filter which are connected to common antenna port, planar coupler for output power monitoring and low pass filter for harmonic attenuation of power amplifier and coaxial cavity resonator. The material and dimensions of the resonator are determined for minimum frequency shift by temperature variation using 3D EM simulation. The measured results of the prototype showed a good agreement with the simulation results, and it should be well applied not only for guided weapon systems but also for any other communication systems such as remote radio head.