• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.2
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• pp.179-188
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• 2015

Testing a radar system in real environment requires a lot of time and cost. Thus various target simulators are developed to evaluate the radar performance and its functions as well. In order to enhance the range resolution and the accuracy for tracking, recent radar system tends to use the wideband signal. In this paper, we summarize two target simulation methods - the direct sampling method with the digital memories and the beat frequency generation for the stretch processing - and suggest the condition to improve their performance for a wideband radar system.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.10
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• pp.2409-2416
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• 2014

In this paper, an automatic recognition algorithm for linearly modulated signals like PSK, QAM under noncoherent asynchronous condition is proposed. Frequency, phase, and amplitude characteristics of digitally modulated signals are changed periodically. By using this characteristics, cyclic moments and higher order cumulants based features are utilized for the modulation recognition. Hierarchial decision tree method is used for high speed signal processing and totally 4 feature extraction parameters are used for modulation recognition. In the condition where the symbol number is 4,096, the recognition accuracy of the proposed algorithm is more than 95% at SNR 15dB. Also the proposed algorithm is effective to classify the signal which has carrier frequency and phase offset.

• Journal of KIISE
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• v.41 no.12
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• pp.1050-1057
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• 2014

Electroencephalogram (EEG)-based brain-computer interfaces (BCI) can be used for a number of purposes in a variety of industries, such as to replace body parts like hands and feet or to improve user convenience. In this paper, we propose a method to decompose and extract motor imagery EEG signal using Empirical Mode Decomposition (EMD) and Fast Fourier Transforms (FFT). The EEG signal classification consists of the following three steps. First, during signal decomposition, the EMD is used to generate Intrinsic Mode Functions (IMFs) from the EEG signal. Then during feature extraction, the power spectral density (PSD) is used to identify the frequency band of the IMFs generated. The FFT is used to extract the features for motor imagery from an IMF that includes mu rhythm. Finally, during classification, the Support Vector Machine (SVM) is used to classify the features of the motor imagery EEG signal. 10-fold cross-validation was then used to estimate the generalization capability of the given classifier., and the results show that the proposed method has an accuracy of 84.50% which is higher than that of other methods.

• The Journal of the Acoustical Society of Korea
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• v.42 no.4
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• pp.320-328
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• 2023

Underwater active target detection is vital for defense systems, requiring accurate detection and estimation of distance and velocity. Sequential transmission is necessary at each beam angle, but divided pulse length leads to range ambiguity. Multi-frequency transmission results in time-bandwidth product losses when bandwidth is divided. To overcome these problem, we propose a novel method using Generalized Sinusoidal Frequency Modulation (GSFM) for rapid target detection, enabling low-correlation pulses between subpulses without bandwidth division. The proposed method allows for rapid updates of the distance and velocity of target by employing GSFM with minimized pulse length. To evaluate our method, we simulated an underwater environment with reverberation. In the simulation, a linear frequency modulation of 0.05 s caused an average distance estimation error of 50 % and a velocity estimation error of 103 % due to limited frequency band. In contrast, GSFM accurately and quickly tracked targets with distance and velocity estimation errors of 10 % and 14 %, respectively, even with pulses of the same length. Furthermore, GSFM provided approximate azimuth information by transmitting highly orthogonal subpulses for each azimuth.

• Journal of Advanced Navigation Technology
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• v.2 no.1
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• pp.22-33
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• 1998

In the coherent-on-receiver radar system using the magnetron source, frequency synthesizer is employed as a STALO(Stable Local Oscillator) to keep the intermediate frequency stable. In this paper, X-band(8.4GHz~9.7GHz) single loop frequency synthesizer is designed and implemented by an indirect frequency synthesis technique. Phase comparison is performed by a digital PLL(Phase-Locked Loop) chip and the loop filter is designed for the low phase noise. The effects of loop component characteristics on the output phase noise are analyzed for single loop structures, and the calculated results are compared with the measured data.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.9
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• pp.1975-1984
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• 1997

In this paper, we analyzed the frequency characteristics and the crosstalk of the adjacent parallel lines and the crossed lines in high-speed packaging interconnections by using the three-dimensional finite difference time domain (3D FDTD) method. To analyze the actual crosstalk phenomena in the transmission of the high-speed digital sgnal, the step pulse with fast rise time was used for the source excitation signal instead of using the Gaussian pulse that is generally used in FDTD. To veify the theoretical resutls, the experimental interconnection lines that were fabricated on the Duroid substrate($\varepsilon_{r}$=2.33, h=0.787 [mm]) were tested by TDR(time domain reflectometry). The results show good agreement between the analyzed results and the tested outcomes.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.12
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• pp.159-164
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• 2005

Recently, it has demanded high-speed digital circuits as information increase. Therefore, electromagnetic characteristics of compact microwave circuit occurred importantly. And, the effect of the imperfect ground plane on the signal integrity and influence of coupling between two parallel lines for high-speed digital transmission line on the printed circuit board is investigated by FDTD simulations in 3-D electromagnetic analysis method. The results of FDTD simulation are compared with the ADS simulation in commercial software, analyzed lumped element of modeling and electromagnetic wave's radiation of slot as frequency. As a consequence, when the slot in the ground plane is under microstrip line, it has much effect on propagation of wave.

• Journal of the Institute of Convergence Signal Processing
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• v.5 no.3
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• pp.216-222
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• 2004

Frequency selective fading is a limiting factor for transmission rate and performance in high-speed multimedia communications. In this paper, we propose a turbo coded adaptive quadrature amplitude modulation (QAM) system for efficient high-speed transmission. By making use of a user-friendly simulation platform of SPW, the proposed turbo coded adaptive QAM system(TuAQAM) is developed and its performance is evaluated in terms of throughput and BER performance. Two channel models having delay spreads of 700ns and 1400ns are created for the simulations. It is shown that the proposed TuAQAM system provides a performance improvement of approximately 3dB and improved throughput for the channel model whose delay spread is 700ns. Similarly, a performance improvement is also achieved for the channel model whose delay spread is 1400ns.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.3
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• pp.333-341
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• 2015

In this paper, a 0.5~4 GHz frequency synthesizer having good phase noise performance is proposed. Wideband output frequencies of the synthesizer were synthesized using DDS(Direct Digital Synthesizer) and analog direct frequency synthesis technology in order to obtain fast settling time. Also in order to get good phase noise performance, 2.4 GHz DDS clock was generated by VCO(Voltage Controlled Oscillator) which was locked by the 100 MHz reference oscillator using SPD(Sample Phase Detector). The phase noise performance of wideband frequency synthesizer was estimated and the results were compared with the measured ones. The measured phase noise of the frequency synthesizer was less then -121 dBc @ 100 kHz at 4 GHz.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.1
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• pp.384-389
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• 2011

This article presents an ultra broadband resistive power divider circuit for smart grid applications. Since the future smart grid system is expected to deploy high speed power line communication, the frequency response of the resitive power divider circuit is naturally of significance. Employing a thin film technology, the resistive power divider was designed, measured, and fabricated. For the circuit design, the conductor-backed coplanar waveguide line was firstly designed and measured. The 3 dB cutoff frequency was 72 GHz and S11 remains <-20 dB upto 70 GHz. The fabricated resistive power divider shows the 3 dB cutoff frequency of 50 GHz. It was experimentally verified that the resistive power divider circuit shows the insertion loss of 6 dB for high-speed input signal (40 Gb/s).