• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2C
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• pp.213-221
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• 2004

A new method for design of two-channel finite-impulse response(FIR) quadrature mirror-image filter(QMF) banks with low reconstruction delay using weighting function is proposed. The weighting function used in this paper is calculated from the previous updated filter coefficients vector which is adjusted from iteration to iteration in the design of QMF banks. In this paper, passband and stopband edge frequency are used in design of QMF banks with low delay characteristic in time domain instead of specific frequency interval where the artifacts occur in conventional design method. The investigation of specific frequency interval where artifacts occur can not be required by using passband and stopband edge frequency. Some comparisons of performance are made with other existing design method to demonstrate the proposed method for QMF bank design. and it was observed that the proposed method using the weighted function and passband and stopband edge frequency improves the peak reconstruction error by 0.001 [dB], the peak-to-peak passband ripple by 0.003[dB], SNR with a white noise by 7[dB] and SNR with a step input by 32[dB], but with a reduction of the computational efficiency because of updating the weighting function over the conventional method in Ref [11].

• Proceedings of the KIEE Conference
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• 2004.07d
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• pp.2164-2166
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• 2004

QFT는 플랜트의 변동을 고려하여 주파수 영역에서 설계하는 제어기법으로 파라미터의 변화 및 외란에 강인한 제어기 설계에 적합한 제어기 설계 방법이다. 본 논문에서는 종축 방향의 항공기 무게 중심이 변화하는 범위에 대하여 요구 비행성(Flying Quality)을 만족하도록 하는 강인한 QFT 제어기의 설계기법을 제안하였다. 시뮬레이션을 통하여 제안한 QFT 제어기가 무게중심의 변화 범위에서 주어진 비행성능을 만족함을 확인하였다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.7 no.1
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• pp.26-35
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• 1996

In this paper, characteristics of the electromagnetically coupled broadband microstrip antennas are analyzed by the Finite Difference Time Domain (FDTD) method, and antenna para- meters are optimized to get maximum bnadwidth. By using short radial tuning stub in microstrip feedline, electromagnetically coupled microstrip antenna shows broadband ($\simeq$13%) characteristics, and the characteristics are varied as a function of radius, radial angle, and position of the radial tuning stub. Operating frequency, return loss, VSWR and input impedance are calculated by Fourier transforming the time domain results. After optimization of the parameters, maximum bandwidth of the radial stub tuning microstrip antenna is about 15% and the ripple char- acteristic of the VSWR is better than the rectangular tuning stub microstrip antenna.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.12
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• pp.32-37
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• 2000

We proposed to a new method of the aperture coupled microstrip antenna with T-shaped feeding slot. We analyzed method of enhancing the bandwidth of the antenna using FDTD. And the antenna parameters are optimized to get maximum bandwidth. We also calculated the progress process of waves and the distribution of electric field in the time domain. We also calculated return loss, VSWR, input impedance, radiation pattern in the frequency domain by Fourier transforming the time domain results, respectively. It was found that the bandwidth of this antenna changes length and width of the patch, length and width of the slot, length of T-shaped feedline, position of the offset. Measured % bandwidth was 49.2 % in the center frequency 2.5 GHz. These results were in relatively food accordance with calculated values.

• The Journal of the Acoustical Society of Korea
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• v.16 no.3
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• pp.73-80
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• 1997

This paper describes structural optimization of optical fiber-wound mandrel hydrophones with Finite Element Method (FEM). The hydrophone is supposed to have operation frequency range of up to 10 kHz and show omni-directional sensitivity pattern at 5 kHz. Studied parameters are mandrel geometry, molding thickness, and material properties of constitutional parts of the hydrophone. Theoretical calculation result shows that pressure sensitivity of the hydrophone increased as either mandrel length or molding thickness gets larger. Also higher pressure sensitivity requires a mandrel or molding material with relatively low Youngs modulus or Poissons ratio. Hydrophone bandwidth increases either as the mandrel length becomes shorter or as the mandrel becomes harder. The omni-directional characteristic is improved as the mandrel length becomes shorter, at 5 kHz. With the above results, we determine the structure of an optical fiber-wound mandrel hydrophone which has the pressure sensitivity of $30 {\times} 10_{-7}$ Rad./Pa, operation frequency range of up to 10 kHz, and shows omni-directional sensitivity pattern at 5 kHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.8 s.111
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• pp.732-738
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• 2006

Divide-by-2 and divide-by-4 circuits which can operate up to 10 GHz are designed. A design method used in these circuits is the TSPC(True Single Phase Clocking) topology. The structure of the TSPC dividers is very simple because they need only a single clock and purely consist of smalt sized cmos devices. Through measurements, we find the fact that in proportion to the bias voltage, the free running frequency increases and the operation region also moves toward a higher frequency region. For operating conditions of bias voltage $3.0{\sim}4.0V$, input power 16dBm and dcoffset $1.5{\sim}2.0V$, 5 GHz and 2.5 GHz output signals divided by 2 and 4 are measured. The layout size of the divide-by-2 circuit is about $500{\times}500 um^2$($50{\times}40um^2$ except pad interconnection part).

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.2
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• pp.223-228
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• 2007

The Digital Frequency Synthesizer(DFS) that generates the wideband signal with high speed frequency hopping rate and high frequency resolution characteristics was designed and implemented in this paper The DFS was applied as local oscillator for direct frequency conversion IF modules of DVB-RCS, which directly generates the transmission immediate frequency signal by using DDS and wideband PLL technologies. The DDS technology provides high speed frequency hopping rate and high frequency resolution characteristics, which are also the DVB-RCS requirement. The wideband PLL technology also provides the wideband signal generation, which is a necessity for direct frequency conversion modules. The implemented DFS provides the spurious suppression characteristic of -50 dBc and less, frequency resolution of 0.233 Hz and frequency hopping rate of 125 ns, respectively. Also the DFS represents the amplitude flatness of 3 dB and less in the pass-band, and phase noise characteristic of -75 dBc/Hz at 1 kHz frequency offset.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.7 no.5
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• pp.430-439
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• 1996

In printed circuit board (PCB) design, it is necessary to predict the crosstalk effect among traces on the circuitary behavior. In this paper, crosstalk between parallel or crossing traces was treated by the finite difference time domain (FDTD) method. They are the typical models of PCB traces and the crosstalk is a major contributor in the creation of electromagnetic interference (EMI). The crosstalk effect was computed for the variation of distance spacing and length of parallel traces and crossing traces. The results in time and frequency domain are discussed and compared with those using MDS(microwave design system) and HFSS(high frequency structure simulator). The comparison shows that the FDTD method can be of wide application in analysis model and save the time required for calculation.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.7
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• pp.3-9
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• 2015

In this paper, we propose an initial timing and frequency synchronization scheme for low probability detection (LPD) systems with cyclic code shift keying (CCSK). The performance of the LPD system with CCSK highly depend on initial timing and frequency offset. On the other hand, the operating SNR (Signal-to-Noise Ratio) of LPD systems is usually very low. Hence, to guarantee a reliable performance of the LPD system, it is crucial to develop suitable initial synchronization algorithms. In this paper, we propose an initial timing and frequency synchronization scheme suitable for CCSK based LPD system using a repeated preamble pattern.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.16 no.5
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• pp.434-444
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• 1991

An improved 2-D quadrature polar separable (QPS) filter and its applications to texture processing are discussed in thie paper. The frequency response of the filter consists of two independent parts. The first is a radial weighting function based on the prolate spheridal sequence(PSS). The second is the same orientational function of the angle as in the Knutsson filter. The new filter is suboptimal in the energy loss because we let the polar angle function approximate the radial weighting function as in the 2-D Cartesian filter composed of two PSS's. It is easy to control as it depends only upon the design specification of the bandwidth, the drectional agnle, and the central freqneucy. Also the filter is circularly more symmetric in the frequency domain than the Knutsson filter. In order to estimate the orientation and the frequency component of loca textures in the frequency domain, some applications of the new filter, such as the generation of synthetic textures, the estimation of texture orientations, and texture segementations, are discussed.