• Korean Journal of Optics and Photonics
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• v.9 no.3
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• pp.181-185
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• 1998

Gain characteristic of concatenated erbium-doped fiber amplifiers(EDFA) are studied with a recirculating EDFA loop. For a non-flat gain EDFA, the 3 dB gain bandwidth was reduced to 6 nm after the 20th EDFA. However, for an optimized gain flattened EDFA, in a simple configuration, the 5 dB gain bandwidth was found to be 9nm, even after the 100th EDFA, corresponding to 8000km transmission. This results suggest that the simple optimized flat gain amplifier could be a good candidate for ultra-long distance wavelength division multiplexed transmissions.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.1
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• pp.52-59
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• 2009

In modern radars, dynamic range requirements far severed due to high CNR(Clutter-to-Noise Ratio) environment operation scenario. ADC spurious signal restricted the required dynamic range. In this paper, receiver gain of active phased array radar dependent on ADC nonlinear characteristic was analyzed. Within limited scope of ADC SFDR which blocks required system dynamic range, ADC dynamic range reaches trade-off with ADC SNR loss. Comparing antenna stage output noise voltage to that of ADC input, receiver gain was mathematically analyzed. Finally the whole contents were explained from the application example.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.1149-1152
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• 1999

A gain controllable precision full-wave rectifier for the measurements of small-signal voltage is presented. It consists of gain controllable inverter superdiode and noninverter superdiode. The results of simulation with PSpice and experiment on breadboard show that the proposed rectifier has the characteristic of precise rectification and amplification for small signal voltage.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.5
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• pp.480-492
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• 2009

In this paper, we proposed a broadband U-shaped RFID tag antenna with near-isotropic characteristic at UHF band. The proposed tag antenna is composed of the U-shaped half wavelength dipole and a rectangular shaped feed. The rectangular shaped feed that is located inside U-shaped dipole is connected for conjugate impedance matching with the commercial tag chip. A better constant gain deviation characteristic in the operating frequency band is achieved by inserting a rectangular slit in the lower center of the U-shaped antenna body. On the condition of VSWR<2, the tag antenna had the measured bandwidth of 10.36%, from 860.5 to 954.5 MHz, and 9.84%, from 864.5 to 954 MHz, for antenna without slit and with slit, respectively. On the condition of VSWR<5.8, the tag antennas had the measured bandwidth of 15.78%, from 835.5 to 979.5 MHz, and 15.89%, from 837 to 981.5 MHz, for antenna without slit and with slit, respectively. The difference between the maximum and minimum gain deviations of tag antenna without slit in the operating frequency band is 0.53 dB since the maximum and minimum gain deviations are 3.86 dB and 3.33 dB, respectively. Whereas the difference between the maximum and minimum gain deviations of tag antenna with slit in the operating frequency is 0.06 dB since the maximum and minimum gain deviations are 3.60 dB and 3.54 dB, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.840-843
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• 2001

In this study, temperature dependency of current gain for AlGaAs/GaAs/GaAs HBT is analytically proposed over the temperature range between 300K and 600K. Energy bandgap, effective mass, intrinsic carrier concentration are considered as temperature dependent parameters. Collector current which is numerically calculated is then analytically expressed to enhance the speed of calculation for current gain. From the results, current gain decreases as the temperature increases. These results will be used to expect the unity current gain frequency f$_{T}$ in conjunction with emitter-base and collector- base capacitances.s.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.271-272
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• 2006

This paper presented a new experimental gain tuning technique for a Multi-Axis Servo System. First, the investigation for proportional gain of velocity control loop by using a Dynamic Signal Analyzer (DSA) was performed. Using the FUNCTION characteristic of DSA based on the Bode plot, the Bode plot of open loop transfer function was obtained. In turn, the integral gain of a servo controller can be found out by using the Integration time constant extracted from the Bode plot of open loop transfer function. In the meanwhile, the positional gain of the servo controller has been obtained by using the Bode plot of the closed loop transfer function. We have also proposed the technique to find out an optimal parameter of a notch filter, which has a great influence on vibration reduction, by using the damping factor extracted from the Bode plot of closed loop transfer function.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.6
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• pp.1221-1226
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• 2011

In order to analyze the receiver gain characteristic of the Soret-type FZPL lens antenna which is operated at 12GHz, TLM method can be applied. The application of the FZPL lens antenna is often use the receiver for satellite TV system, radio telescope, and Geodetic System. Some numerical results computed by TLM method are compared with Kirchhoff's approximation and PO method. The focal characteristic of receiver gain on main axis of the FZPL is mostly shown at the front side, which means that the position of the receiver should be properly calibrated.

• Proceedings of the KIPE Conference
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• 2007.07a
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• pp.98-100
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• 2007

This paper proposes a robust digital controller for PWM voltage source inverter using CRA method. The usual inverter controller for the operation of constant voltage and constant frequency consists of a double looped PI controller for the outer voltage controller and the inner current controller, of which the order of characteristic polynomial is high and so the gain tuning is difficult. Considering the limited switching frequency of the devices and sampling frequency of the digital controller, the gain tuning is usually based on the engineering experiences with the try and error method. In this paper, the error-space approach is used to get the system model including the controller with low order, and the characteristic ratio assignment (CRA) method is proposed for the design of robust controller which has the advantage to design the optimal gain to meet the referenced response and overshoot within the limit range. The PSiM simulation and experience results are shown to verify the validity of the proposed controller.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.7
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• pp.784-795
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• 2007

In this thesis, the Multi element antenna with wideband and enhanced gain characteristic is proposed to operate at both frequency range from 824 MHz to 896 11Hz for the CDMA and frequency range from 908.5 MHz to 914 MHz for the RFID band. The proposed antenna has tile size of $35{\times}15{\times}5mm^3$ in order to put it in the A model of S company and each element of the proposed antenna is folded to obtain the minimum size. To obtain the antenna with wideband and high gain characteristic, the radiator of the antenna is divided into 4 elements. As a result, bandwidth of the proposed antenna become broader and lower center frequency is appeared due to increased and lengthened current path. Moreover, the enhanced gain characteristic is verified because divided element structure that induct uniform current distribution can get increased antenna efficiency. To attain more uniform current distribution, modified structure of the feeding point that can deliver currents directly is designed. The antenna that alters the feeding structure has higher gain value. Each element is folded to increase the current paths considering the current directions to attain the miniaturization of the antenna. To measure the handset antenna, the handset case must be considered. Even though antenna is designed for predicted characteristic, the resonance frequency is shifted and antenna gain is deteriorated at predicted frequency while antenna is set in the handset case. 1.08 GHz of the resonant frequency is determined after frequency shift from 150 MHz to 200 MHz is confirmed and the maximum gain is measured as 3.1 dBi while antenna is not set in the handset. In case handset case is considered, the experimental results show that the impedance bandwidth for VSWR<2 is from 0.824 GHz to 0.936 GHz(110 MHz). This result appears that the proposed antenna can cover both CDMA and RFID band at once. The measured gain is from -3.4 dBi to -0.5 dBi and it has omni-directional pattern practically.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.2
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• pp.147-153
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• 2009

In this paper, FSS(Frequency Selective Surface) using defect mode characteristic is proposed. The unit cell using defect mode characteristic of the proposed FSS is offered lower resonant frequency in the same cell size. The number of suitable array is optimized 13 by 13. Also, the patch antennas operated in WCDMA(Wideband Code Division Multiple Access) Tx band and Rx band are designed for the comparison. The gain value of proposed FSS-1 complex structure (the patch antenna of Tx band and FSS) is improved 3.3 dB from 9.98 dBi to 13.28 dBi in Tx band. The gain value of proposed FSS-2 complex structure(the patch antenna of Rx band and FSS) is improved 5.53 dB from 9.81 dBi to 15.34 dBi in Rx band. Also the measured impedance bandwidth($VSWR{\leq}2$) of manufactured $13{\times}13$ array antenna is from 337 MHz(1.87 to 2.21 GHz). The measured radiation gain is 11.39 dBi(1.94 GHz), 13.11 dBi(2.05 GHz), 11.09 dBi(2.14 GHz). The measured radiation efficiency is 81 %. Because the proposed FSS structure has more higher gain, it will be applied to antenna of WCDMA repeater system.