• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.1 s.92
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• pp.49-55
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• 2005

In this paper, the phase locked harmonic oscillator(PLHO) using the analog PLL(Phase Locked Loop) is designed and implemented for a wireless LAN system. The harmonic oscillator is consisted of a ring resonator, a varactor diode and a PLL circuit. Because the fundamental fiequency of 8.5 GHz is used as the feedback signal for the PLL and the 2nd harmonic of 17.0 GHz is used as the output, a analog frequency divider for the phase comparison in the PLL system can be omitted. For the simple PLL circuit, the SPD(Sampling Phase Detector) as a phase comparator is used. The output power of the phase locked harmonic oscillator is 2.23 dBm at 17 GHz. The fundamental and 3rd harmonic suppressions are -31.5 dBc and -29.0 dBc, respectively. The measured phase noise characteristics are -87.6 dBc/Hz and -95.4 dBc/Hz at the of offset frequency of 1 kHz and 10 kHz from the carrier, respectively.

• The Transactions of the Korean Institute of Power Electronics
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• v.11 no.4
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• pp.313-320
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• 2006

In this paper, a design approach of LC trap filter for output side harmonic reduction of single phase NPC multilevel inverter is proposed, and THD of the output voltage and harmonic FFT of the output current are analyzed. The proposed filter consists of a conventional LCR filter cascaded with an LC trap filter and it is tuned to inverter switching frequency. A NPC multilevel inverter inverter is used an inverter system for high power application and DSP(TMS320C31) is used for the controller. The effectiveness of the proposed system confirmed through simulation and experimental results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.7
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• pp.1182-1190
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• 2001

In this paper, microstrip photonic bandgap (PBG) structure with special perforation patterns etched on the line itself is analyzed and optimized in shape, then used for harmonic tuning of power amplifier. This PBG has an advantage in being fabricated and grounded. The dimension of unit lattice is enlarged vertically, but its input and output line maintain 50 Ω using tapered line. This modification from original structure can lessen possible error in etching PCB. The analysis and design of PBG structure are acquired from using EM simulation. The measured insertion loss of the final structure is 0.3 ∼0.4 dB, and its bandwidth of stopband is 6∼7 GHz. Measured results of improved characteristics by using PBG structure at the output of the power amplifier are 0.72∼0.99 dB in output power, 1.14∼7.8 % in PAE, and 1 dBc in the third IMD.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.11B
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• pp.1612-1619
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• 2001

This paper examines the design, implementation characteristics of a folded dipole active integrated antenna. Our goal was to minimize the physical size of RF circuit and its insertion loss, and to make the high frequency tuning easier by directly integrating the ISM(Industrial Scientific & Medical) band power amplifier and antenna. Non-linear model has been used for highly accurate simulation of the power amplifier. The maximum power level was found by using the Load pull method before an impedance matching was achieved. It is found that the total power-added efficiency(PAE) including the driving amplifier was 31.5% and that the transmit power was 13.7 dBm. We also found that the proposed scheme with the smaller antenna as compared with the existing dipole antenna has 23.7 dB total gain including the antenna gain. The suppression of the second harmonic signal to the fundamental signal with respect to the fundamental signal was found to be more than 30 dBc.

• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.1
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• pp.75-85
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• 2010

In this paper, a Z-source hybrid active power filter is proposed to compensate the harmonics and reactive power in power distribution system. The proposed system is composed of a 7th harmonics-tuned passive filter and an active power filter with a Z-source inverter topology, while voltage source PWM inverter or current source PWM inverter are applied as the power converter topology of conventional active power filters. The Z-source impedance network along with shoot through capability would ensure a constant DC voltage across the DC link. A polymer electrolyte membrane fuel cell is employed as an compensation DC energy source of the proposed system and its equivalent R-L-C circuit is modeled for simulation. As the compensation and control algorithm of the proposed system, the current synchronous detection algorithm is applied. The simulation analysis by PSIM is performed under the three-phase 220V/60Hz voltage source and 25A nonlinear diode loads. The effectiveness of the proposed the system is verified in the steady and transient states.

• Proceedings of the KIEE Conference
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• 2006.07a
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• pp.460-461
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• 2006

Computer Loads can be found in all of modern society. The switching mode power supplies used in personal computers are major sources of harmonic currents. Harmonic currents can cause lots of harmonic problems such as disruption in computer performance. A series resonant filter is very effective in harmonic reduction for personal computer loads. Voltage sags are short duration reductions in rms voltage. The main causes of voltage sags are faults, motor starting, and transformer energizing. Personal computers are another example of devices sensitive to voltage sags. A serious voltage sag at the terminals way lead mis-operation of the equipment. This paper presents an in depth analysis to evaluate the effect of harmonics reduction based on the IEC 61000-3-2 and the effect of voltage sag using ITI curve by applying a series resonant filter for personal computer loads.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.5
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• pp.468-474
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• 2010

In this paper, a VCHO(Voltage Controlled Harmonic Oscillator) for K-band application has been designed and implemented. The proposed oscillator has a structure of two hair-pin resonators placed on input and output of active device. Using in/out common frequency tuning structure, the VCHO yields some advantages of the enhanced fundamental frequency suppression characteristic as well as the improved output power of second harmonic. According to implementation and measurement results, it was shown that a VCHO provides an output power of -2.41 dBm, a fundamental frequency suppression of -21.84 dBc, and phase noise of -101.44 dBc/Hz at 100 kHz offset. In addition, as for the bias voltage from 0 V to -10 V for the varactor diode, output frequency range of 10.58 MHz is obtained with a power variation of ${\pm}0.19\;dB$ over its frequency range.

• Journal of the Korea Society of Computer and Information
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• v.3 no.4
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• pp.35-43
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• 1998

This study has been experimented the characteristics of synchronous oscillator for clock recovery of Direct Sequence/Spread Spectrum(DS/SS) communication. When external wave is not provided, The Synchronous Oscillator(SO) oscillates at its natural frequency. As soon as external signal is applied, the SO starts tracking the external frequency which can be sinusoidal, pulsed or some other waveform. Thus, the output is synchronized with the range of wide tracking bandwidth to the external frequency Specifically, the SO also posses frequency division and multiplication capability. All of these indicate that the SO can overcome difficulties to get synchronization in coherent digital communication systems. We make a practical application of DS/SS communication with study on the synchronous properties of SO. As the result, we have a good performance.

• Journal of the Korean Institute of Telematics and Electronics T
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• v.35T no.1
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• pp.90-98
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• 1998

This paper is to describe the improved vector control which can control the induction motor robustly in low speed. When the induction motor is drived with low speed, below 10 percent of the rated speed, an algorithm which can compensate the error of unit vector angle generated by the harmonics is proposed. Another algorithm which can be tuned to the rotor time constant so that nay be robust to the rotor parameter change in low speed and transient state was proposed. The ripple of flux and torque was reduced by the proposed vector control and then the stable output characteristics was obtained in low speed. When the input and output is sinusoidal, the proposed vector control, the direct vector control and the indirect vector control were analyzed and compared in the low speed characteristics. And each control characteristics is compared and analyzed in state of containing harmonics. The estimation and tunning performance of rotor time constant is confirmed with simulation. The whole control system is implemented by real hardware and experimented to compare the proposed vector control with the direct vector control. As a result of the experiment with two control methods in low speed, the torque ripple of the proposed vector control is improved by 45 percent than the direct vector control. And it is confirmed that the flux current ripple is reduced in 0.2 p.u. and torque current ripple is reduced in 0.6 p.u. It is confirmed that the rotor time constant by the estimation and the tunning algorithm is tunned by the real rotor time constant. Finally, it was confirmed that the validity and robustness for the proposed vector control in low speed existed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.11
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• pp.1075-1081
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• 2004

In this paper, a VCO of a general advance warning system for vehicle's speed limitation in the X-band used in Japan is designed using a small signal scattering coefficient of PHEMT. A varactor diode that wide tuning range and series resistance 0 H is used for designing the VCO and -85 dBc/Hz of phase noise at 10 kHz of offset frequency is obtained by adjusting the reflection coefficient between the micro-strip line and the varactor device which determines transistor's operation voltage and resonant frequency, In addition +4.5 dBm of basic frequency signal output level and -25.6 dEc of the second harmonic constraint are acquired. Sample that produce in this paper could confirm that more excellent special quality appears than existing products in sensitivity.