• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.5
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• pp.359-365
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• 2018

Herein, electromagnetic shielding structures to reduce the external noise coupling to printed spiral coils (PSCs) and a design method for improving the bandwidth of shielded PSCs have been proposed. It has been demonstrated that the bandwidth of shielded PSCs is limited due to the parasitic capacitance between the coils and the shielding structures and is confirmed by the transfer function simulation of the shielded PSCs with a transmission line as the radio-frequency interference noise source. A design method for the bandwidth improvement of the shielded PSCs has been proposed based on the equivalent circuit model analysis and the case studies depending on PSC designs with a three-dimensional field simulation. With the design method, an optimized shielded PSC design has been presented and successfully confirmed by experimental verification in that the optimized design results in a significant bandwidth improvement.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.2
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• pp.244-249
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• 2008

In this paper, we designed and fabricated the EM wave absorber consists of Sendust and Mn-Zn ferrite for suppressing EM wave noise from PCB in ISM(Industrial, Scientific and Medical) band of 2.4 GHz. We fabricated several samples in different ratios of Sendust to Mn-Zn ferrite with CPE(Chlorinated Ploy-ethylene) as binder and confirmed that optimum composition ratio of absorbing materials was Sendust. Mn-Zn ferrite : CPE=70:5:20 wt.%. The absorbing abilities were simulated according to different thickness of EM wave absorber as the function of material constants calculated by measured data. Measured absorption ability was analyzed and compared with simulated result. The simulated result agree well with the measured ones. As a result, the developed EM wave absorber with thickness of 0.85 mm has absorption ability of 5.4 dB at 2.4 GHz and over 3 dB in frequency rage of 1.4$\sim$4.1 GHz.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.1
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• pp.23-28
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• 2011

In this paper, we propose a channel selection scheme for secondary users in cognitive radio sensor networks, which includes learning automata and fuzzy logic system (FLS). In the proposed scheme, FLS is used as the channel selection mechanism while the learning automata algorithm is being used to learn the radio environment such as channel link quality. Signal to noise ratio of the link between primary user (PU) and secondary user (SU), the probability of choosing channel, and signal to noise ratio of the link between secondary users are chosen as input parameters for the FLS to decide one data channel among multiple channels. Simulation results show that the proposed scheme does indeed provide advantages in improving the throughput of CR networks, in comparison with some other previous schemes.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.3 s.106
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• pp.239-248
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• 2006

In this paper, the cryogenically cooled low noise amplifier module for radio telescope receiver front-end using pHE-MT MMIC is designed and fabricated. In the selection of MMIC, the MMIC fabricated with the pHEMTS providing successful cryogenic operation are chosen. They are mounted in the housing using the thin film substrate. In the design of the housing, the absorber and the elimination of the gap between the carrier and the housing as well removed the unnecessary oscillations by its structure. The mismatch is improved by ribbon-tuning to provide the best performance at room temperature. The fabricated module shows the gain of $35dB{\pm}1dB$ and the noise figure of $2.37{\sim}2.57dB$ at room temperature over $21.5{\sim}23.5GHz$. In the cryogenic temperature of $15^{\circ}K$ cooled by He gas, the measured gain was above 35 dB and flatness ${\pm}2dB$ and the noise temperatures of $28{\sim}37^{\circ}K$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.4
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• pp.453-461
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• 2011

In order to use more efficiently limited frequency resources at the broadcasting band and to eliminate blanket area of the terrestrial broadcasting and to improve broadcasting quality. The importance of repeaters has increasing continuously. However, in case of T-DMB digital on channel repeater in OFDM systems, some of the signal radiated feedback again at the receiver antenna. So it generates feedback signal interference in repeater system. Also phase noise increases ICI(Inter Carrier Interference). It affects seriously the frequency domain equalizer. In this paper, we remove the feedback signal interference by LMS with correlation. Also we propose an effective equalizer algorithm that can remove ICI caused by phase noise and the power amplifier's back-off. In this simulation results, this system is satisfied the performance of BER=$10^{-4}$ at less than SNR=14 dB after compensation of phase noise.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.6
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• pp.75-82
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• 2018

In this paper, we consider a precoder design for downlink multiuser multiple-input multiple-output (MU-MIMO) in distributed antenna systems (DAS). In DAS, remote radio heads (RRHs) are placed at geographically different locations within a cell area. Three different precoder design schemes are proposed to maximize the separate or joint signal-to-leakage-plus-noise ratio (SLNR) metrics by considering RRH sum power or per-RRH power constraints. The analytical closed-form form solution for each optimization problem is presented. Through computer simulation, we show that the joint SLNR based precoding schemes have better signal-to-interference-plus-noise ratio (SINR) and bit error rate (BER) performances than the separate SLNR based schemes. Also, it is shown that the precoding scheme with RRH sum power constraint has better performance than the precoding scheme with per-RRH power constraint.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.8
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• pp.737-743
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• 2004

A fixed-tuned SIS(Superconductor-Insulator-Superconductor) mixer across 120∼180 GHz band has been developed. This mixer employs an SIS chip fabricated by Nobeyama radio observatory which consists of a series array of 6 Nb/Al-Al$_2$O$_3$/Nb junctions in a microstrip line on a fused quartz substrate. The SIS chip is placed at the center of the half-height waveguide mixer mount to have a good incoming signal coupling over the whole frequency band. No mechanical tuner was used in the SIS mixer and the RF signal and local oscillator power are injected to the mixer via a cooled cross-guide coupler. In order to prevent the IF signal loss, the If output impedance of the SIS mixer was matched to the 50 $\Omega$ input impedance of the IF chain. Measured double sideband noise temperatures of a receiver using the SIS mixer are 32∼131 K over 120∼180 GHz band. The developed SIS mixer is now in use for radio astronomical observations on the TRAO 14 m radio telescope.

• Journal of Astronomy and Space Sciences
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• v.28 no.4
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• pp.267-271
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• 2011

I developed an enhanced correction method for Ricean bias which occurs in linear polarization measurement. Two known methods for Ricean bias correction are reviewed. In low signal-to-noise area, the method based on the mode of the equation gives better representation of the fractional polarization. But a caution should be given that the accurate estimation of noise level, i.e. ${\sigma}$ of the polarized flux, is important. The maximum likelihood method is better choice for high signal-to-noise area. I suggest a hybrid method which uses the mode of the equation at the low signal-to-noise area and takes the maximum likelihood method at the high signal-to-noise area. A modified correction coefficient for the mode solution is proposed. The impact on the depolarization measure analysis is discussed.

• Journal of electromagnetic engineering and science
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• v.8 no.3
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• pp.114-118
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• 2008

Direct-conversion RF front-end for 5-GHz WLAN is implemented in $0.18-{\mu}m$ CMOS technology. The front-end consists of a low noise amplifier, and low flicker noise down-conversion mixers. For the mixer, an inductor is included to resonate out parasitic tail capacitances in the transconductance stage at the operating frequency, thereby improves the flicker noise performance of the mixer, and the overall noise performance of the front-end. The receiver RF front-end has 6.5 dB noise figure, - 13 dBm input IP3, and voltage conversion gain of 20 dB with the power consumption of 30 mW.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.4
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• pp.761-767
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• 2007

In this paper, we deal wih a concurrent dual band low noise amplifier for a Radio Frequency Identification(RFID) reader operating at 912MHz and 2.45GHz. The design of the low noise amplifier is based on the TSMC $0.18{\mu}m$ CMOS technology. The chip size is $1.8mm\times1.8mm$. To improve the noise figure of the circuit, SMD components and a bonding wire inductor are applied to input matching. Simulation results show that the 521 parameter is 11.41dB and 9.98dB at 912MHz and 2.45GHz, respectively The noise figure is also determined to 1.25dB and 3.08dB at the same frequencies with a power consumption of 8.95mW.