• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.7
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• pp.67-71
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• 2008

We report the waveguide to microstrip transition using probe structure for Ka-band transceiver. The waveguide to microstrip transition is composed of probe, inductive line, ${\lambda}/4$ impedance transformer, and $50{\Omega}$ microstrip line. For design of the transition, we optimized the characteristic impedances and the lengths of the component parts. The fabricated transition exhibits an insertion loss of 1.3 dB and the input/output return losses of below 14 dB between 30 and 40 GHz. The insertion loss of each transition is about $0.5{\sim}0.6dB$, considering the losses in the microstrip line and input/output waveguides.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.2
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• pp.162-172
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• 2011

In this paper, a design and fabrication of 4 W power amplifier for the WiMAX frequency band(2.3~2.7 GHz) are presented. The adopted active device is a commercially available GaN HEMT chip of Triquint Company, which is recently released. The optimum input and output impedances are extracted for power amplifier design using a specially self-designed tuning jig. Using the adopted impedances value, class-F power amplifier was designed based on EM simulation. For integration and matching in the small package module, spiral inductors and interdigital capacitors are used. The fabricated power amplifier with $4.4{\times}4.4\;mm^2$ shows the efficiency above 50 % and harmonic suppression above 40 dBc for second(2nd) and third(3rd) harmonic at the output power of 36 dBm.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.10
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• pp.1364-1370
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• 2014

Power system fault analysis has been based on symmetrical component method, which describes power system elements by positive, negative and zero sequence impedance. Obtaining accurate line impedances as possible are very important for estimating fault current magnitude and setting distance relay accurately. Especially, accurate calculation of zero sequence impedance is important because most of transmission line faults are line-to-ground faults, not balanced three-phase fault. Since KEPCO has started measuring of transmission line impedance at 2005, it has been revealed that the measured and calculated line impedances are well agreed within reasonable accuracy. In case of underground transmission lines, however, large discrepancies in zero sequence impedance were observed occasionally. Since zero sequence impedance is an important input data for distance relay to locate faulted point correctly, it is urgently required to analyze, detect and consider countermeasures to the source of these discrepancies. In this paper, development of pre/post processor to ATP (Alternative Transient Program) version of EMTP (Electro-Magnetic Transient Program) for sequence impedance calculation was described. With the developed processor ATP-cable, effects of ground resistance and ECC (Earth Continuity Conductor) on sequence impedance were analyzed.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.39 no.9
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• pp.44-50
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• 2002

Recently, a envelope tracking(ET) amplifier that improves efficiency by changing of the bias according to the RF input level is presented to use for a high power amplifier of cellular radio handset using CDMA. The input and the output impedances of the ET amplifier may be varied by changing of the bias of the amplifier, and it makes the amplifier having low gain, low efficiency, and high input and output VSWR. In order to improve the input and the output mismatch of the amplifier, in this paper, two types of ET amplifier are suggested. In case of an ET amplifier using varactor diode, in experimentation, gain is improved about 7dB and the power consumption of the amplifier is better about 60% than that of the conventional amplifier. In case of a base voltage controlled ET amplifier, the gain and power consumption of the amplifier is improved about 9dB and 40% than those of the conventional amplifier, respectively.

• Proceedings of the IEEK Conference
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• 2002.07a
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• pp.512-514
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• 2002

The dynamic permittivity of a microstrip structure leads to a convenient and modified Smith-chart representation that includes the frequency-dependent influence of the lossy characteristics of the line cohesively. The efficacy of the model is illustrated with an example concerning a microstrip patch antenna. Relevant simulations show that the input impedances calculated from the model are more accurate than those from the previous model in the literature by comparing to the measure results, as illustrated with an example of a patch antenna. This model is compatible for CAD efforts with MATLAB$\^$TM/ facilitation fast and user-friendly implementations.

• Journal of electromagnetic engineering and science
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• v.17 no.3
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• pp.147-152
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• 2017

This paper presents a frequency doubler operating at G-band that exceeds the maximum oscillation frequency ($f_{max}$) of the given transistor technology. A common-source transistor is biased on class-B to obtain sufficient output power at the second harmonic frequency. The input and output impedances are matched to achieve high output power and high return loss. The frequency doubler is fabricated in a commercial 150-nm GaAs pHEMT process and obtains a measured conversion gain of -5.5 dB and a saturated output power of -7.5 dBm at 184 GHz.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.3
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• pp.177-186
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• 1998

For the purpose of finding out the sound field characteristics in a cavity of a rectangular enclosure with foamed aluminum lining, analytical and experimental studies are performed with random noise input. Experimental method using two-microphone impedance tube measures the absorption coefficients and the impedances of simple sound absorbing materials. Measured acoustical parameters of the test samples are applied to the theoretical analysis to predict sound pressure field in the cavity. The sound absorp- tion effects from measurements are compared to prediction in both cases with and without foamed aluminum lining in the cavity of the rectangular enclosure.

• Journal of electromagnetic engineering and science
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• v.9 no.3
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• pp.146-151
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• 2009

This paper presents a low-loss broadband balun that uses a coplanar waveguide-to-slotline field transformation. It operates over a very wide frequency range and is of compact size since it does not depend on a resonant structure. To analyse imbalance, the coplanar wavelength(CPW) input ground is connected to the CPW output ground through various capacitors to introduce common-mode impedances. As the common-mode impedance increased the imbalance became significantly higher at the higher-frequency band compared with the lower-frequency band. The bias-circuit approach is used to improve the operation bandwidth of the lower-frequency band. The measured results show a passband of 200 MHz to 2 GHz, an insertion loss of less than 0.75 dB, and a size of $20{\times}14\;mm$. The amplitude imbalance is approximately 0.3 dB and the phase imbalance is less than $6^{\circ}$ over the entire operational range.

• Journal of electromagnetic engineering and science
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• v.16 no.4
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• pp.206-209
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• 2016

This letter proposes a reconfigurable directional coupler that uses a variable impedance mismatch reflector to achieve high isolation characteristics in the antenna front end. The reconfigurable coupler consists of a directional coupler and a single-pole four-throw (SP4T) switch with different load impedances as a variable load mismatch reflector. Selection of the load impedance by the reflector allows cancellation of the reflected signal due to antenna load mismatch and the leakage from the input to isolation port of the directional coupler, resulting in high isolation characteristics. The performance of the proposed architecture in separating the received (Rx) signal from the transmitted (Tx) signal in the antenna front end was verified by implementing and testing the reconfigurable coupler at 917 MHz for UHF radio-frequency identification (RFID) applications. The proposed reconfigurable directional coupler showed an improvement in the isolation characteristics of more than 20 dB at the operation frequency band.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.54 no.3
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• pp.127-133
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• 2005

Korean multi-propulsion system consists of a synchronous alternator driven by a gas turbine driving synchronous alternator coupled to a rectifier - DC link - DC/DC converter and traction system based on modification of the G7 high-speed train. The simulation modules include turbine engine system, alternator, rectifier, DC/DC converter and power management module. Simulation for the multi-propulsion system such as a modular is presented in order to confirm the system stability for loads with uncertain input impedances and control loop speeds. This paper deals with various simulation modules with a specific control loop to help the development of the real lame-scaled system.