• Journal of the Korean Magnetic Resonance Society
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• v.9 no.1
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• pp.48-60
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• 2005

Purpose: The purpose of this study was to design and build an optimized birdcage resonator configuration with a low pass filter, which would facilitate the acquisition of high-resolution 3D-image of small animals at 3T MRI system. Methods and Materials: The birdcage resonator with 12-element structures was built, in order to ensure B1 homogeneity over the image volume and maximum filling factor, and hence to maximize the signal to noise ratio (SNR) and resolution of the 3-dimensional images. The diameter and length of each element of a birdcage resonator were as follows: (1) diameter 13 cm, length 22 cm, (2) diameter 15 cm, length 22 cm, (3) diameter 17 cm, length 25 cm. Spin echo pulse sequence and fast spin echo pulse sequence were employed in obtaining MR images. The quality of the manufactured birdcage resonators wes evaluated on the basis of the return loss following matching and tuning process. Results: The experimental MR image of phantoms by the various manufactured birdcage resonators were obtained to compare the SNR in accordance with the size of objects. The size of an object to that of coil was identified by parameters that were estimated from the image of a phantom. First, the diameter of the birdcage resonator was 15cm, and the ratio of the tangerine to the birdcage resonator accounted for approximately 27%. The Q factor was 53.2 and the SNR was 150.7. Second, at the same birdcage resonator, the ratio of the orange was approximately 53%. The SNR and the Q parameter was 212.8 and 91.2, respectively. Conclusion: The present study demonstrated that if birdcage resonators have the same forms, SNR could be different depending on the size of an object, especially when the size of an object to that of coil is approximately 40~80%, the former is bigger than the latter. Therefore, when the size of an object to be observed is smaller than that of coil, the coil should be manufactured in accordance with the size of an object in order to obtain much more excellent images.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.8
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• pp.42-50
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• 2007

This paper presents design methods for dual-frequency(2.4/5.8GHz) active receiving antennas. The proposed active receiving antennas are designed to interconnect the output port of a wideband antenna to the input port of an active device of High Electron Mobility Transistor directly and to receive RF signals of 2.4GHz and 5.2GHz simultaneously where the impedance matching conditions are optimized by adjusting the length of $1/20{\lambda}_0$(@5.8GHz) CPW transmission line in the planar antenna The bandwidth of implemented dual-frequency active receiving antennas is measured in the range of 2.0GHz to 3.1GHz and 5.25GHz to 5.9GHz. Gains are measured of 17.0dB at 2.4GHz and 15.0dB at 5.2GHz. The measured noise figure is 1.5dB at operating frequencies.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.2
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• pp.9-17
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• 2010

Recently, there has been much interest in orthogonal frequency division multiplexing (OFDM) for next generation wireless wideband communication systems. OFDM is a special case of multicarrier transmission, where a single data stream is transmitted over a number of lower-rate subcarriers. One of the main reasons to use OFDM is to increase robustness against frequency-selective fading or narrowband interference. However, in the radio systems it is also important to distortion introduced by high power amplifiers (HPA's) such as solid state power amplifier (SSPA) considered in this paper. Since the signal amplitude of the OFDM system is Rayleigh-distributed, the performance of the OFDM system is significantly degraded by the nonlinearity of the HPA in the OFDM transmitter. In this paper, we propose a canonical piecewise-linear (PWL) model based digital predistorter to prevent signal distortion and spectral re-growth due to the high peak-to-average power ratio (PAPR) of OFDM signal and the nonlinearity of HPA's. Computer simulation on an OFDM system under additive white Gaussian noise (AWGN) channels with QPSK, 16-QAM and 64-QAM modulation schemes and modulator/demodulator implemented with 1024-point FFT/IFFT, demonstrate that the proposed predistorter achieves significant performance improvement by effectively compensating for the nonlinearity introduced by the SSPA.

• Journal of IKEEE
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• v.3 no.1 s.4
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• pp.79-85
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• 1999

In this paper, the resistive mixer for 5.86Hz wireless LAN, main part receiving system, was designed and implemented. The noise characteristics and the linearity in the base band was superior. For the use of local oscillator of mixer, dielectric resonator of stable output and temperature characteristics was designed. For the electrical tuning by the capacitance variation of varactor diode, the microstrip line and magnetic coupling characteristics of the dielectric resonance was used. It was obtained that gain of the proposed resistive mixer containing the RF cable loss, is -13.8dB, the conversion loss of frequency converter is -12 dB, and the output power of local oscillator is 1.67 dBm.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.5
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• pp.558-565
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• 2013

In this paper, modeling and simulation for performance analysis of high resolution SAR system has been carried out in the time, frequency and numeric domain using ADS Ptolemy simulation tool of Agilent corporation. SAR system consists of antenna, controller and transceiver. Error parameters affecting SAR system performances have been defined, modeled and simulated such as phase noise of frequency synthesizer, amplitude and phase characteristic of TWTA, sampling frequency of waveform generator and I/Q imbalance. Finally, the development requirements of SAR system based on the impulse response function have been derived.

• Journal of the Korean Vacuum Society
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• v.20 no.1
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• pp.1-6
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• 2011

A sudden step change is observed in the vertical position readings from beam position monitors (BPMs) mounted at the several sector vacuum chambers of Pohang Light Source. To study the source of this sudden step change, we measured the RF transmission scattering matrix (S21) through the pickup electrodes of BPMs mounted at the both ends of the sector vacuum chamber. The measured $S_{21}$ graph of the sector vacuum chambers suffering sudden step change has a peak in the BPM operation frequency bandwidth. Otherwise that of the other sector vacuum chambers doesn't have a peak. It is shown by the numerical simulation that the peak found in the BPM operation frequency bandwidth corresponds to the longitudinal harmonic of transverse electric resonance mode.

• Journal of the Korean Chemical Society
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• v.41 no.6
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• pp.292-298
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• 1997

An ICP(Inductively Coupled Plasma) emission spectrometer was developed with an axially viewed ICP source incorporated by a 5-turned induction coil and a torch, outer quartz tube of which was 50 mm longer than that used in conventional ICP/AES(Inductively Coupled Plasma Atomic Emission Spectrometry). The Optimization of the system has been performed in terms of the determination of signal-to-noise ratio and background intensity at various rf powers, sample flow rates, argon gas flow rates and cut-off gas flow rates. The spectro-analytical characteristics of the spectrum obtained between 200 and 500 nm was revealed to be similar compared with a vertically viewed ICP source. The detection limit of Pb(Ⅱ) at 220.35 nm was 11 ppb which was 5 times lower than that obtained with a vertically viewed ICP source.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.8
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• pp.1631-1641
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• 2012

A TDMA system in satellite communication has been utilized. Especially DVB-S2 was standardized and now operated in satellite broadcasting system. In this paper, we propose a TDMA frame structure appropriate for special purpose which has the good reliablilty in a poor RF environment even if frequency efficiency is decreased. TDMA frame duration is 12 seconds which is long duration in comparison with general TDMA system with several ms. Designing the frame structure, time and frequency shift in single frame duration are considered. Simulation results show that the proposed frame structure and synchronization method has robust synchronization performance when the terminal is even in low SNR as well as 25 kHz frequency offsets.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.6
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• pp.87-93
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• 2019

We discuss the design of a radiometer using a millimeterwave(Ka-band) seeker. We applied a total power radiometer, thus the radiometer is composed of a IF-drive amp, band-pass filter, detector and an Op-amp additionally. As a radiometer measure a radiated signal of an object which is noise-like, a radiometer is easily affected by the variance of system temperature. To mitigate an adverse effect, we propose a compensation method in a radiometer without brightmess temperature compensation circuits. Through some experiments such like a distinction a target and the background, we have verified that the designed radiometer system has distingushed a car from the ground completely.

• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.6
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• pp.440-448
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• 2009

Facility power-line electromagnetic interference (EMI) filters are used to provide radio frequency(RF) isolation between dedicated power distribution services and noise sensitive local power distribution systems. This type of EMI filters generally needs a high current capacity and, in some special applications, a high insertion loss of a minimum 100dB from 14kHz through 10GHz per MIL-STD 220 is required. This paper deals with an analysis and design of a wideband facility power-line EMI filter with the above requirements. The characteristics of the inductor and capacitor at high frequencies are investigated. The characteristics and design method of the facility EMI filter with a high order LC network are also presented. The prototype filter is finally implemented and its performance is verified from the experimental results.