• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.9
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• pp.1042-1047
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• 2012

In order to obtain balanced ports matching and isolation between balanced ports of a Marchand balun, a compact isolation network is proposed. The proposed compact isolation network is designed using composite right/left-hand (CRLH) transmission line and compact phase inverter using CRLH transmission line unit cell. Also, design method and analysis of proposed isolation network are presented. The sizes of the proposed isolation networks are significantly reduced to $0.11{\lambda}_g$ and $0.07{\lambda}_g$ compared with the conventional isolation network of $0.5{\lambda}_g$. The Marchand balun is operated at 2.45 GHz and is demonstrated through excellent experimental results.

• Journal of IKEEE
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• v.5 no.1 s.8
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• pp.16-23
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• 2001

Passive noise reduction is a classical approach to attenuate industrial noise, and an active noise cancellation has several advantages over the passive noise cancellation. The active noise reduction system offers a better low frequency performance with a smaller and lighter system. This paper presents a simple active closed loop control system which consists of an controller for inverting and compensating the phase delay, a microphone for picking up the external noise, and a loudspeaker for radiating the acoustic out of phase signal to reduce the external noise, and external noise can be reduced after compensating the phase difference to be $180^{\circ}$ in the frequency of maximum value in the amplitude response. The noise of the phase delay covered from $50^{\circ}\;to\;310^{\circ}$ tends to be reduced in the active noise control system and it is possible to obtain a noise cancelling of up to approximately 20[dB] at the ears in the enclosurer.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.5C
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• pp.498-504
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• 2009

A high-performance low-complexity decoding algorithm for LDPC codes is proposed in this paper, which has the advantages of both bit-flipping (BF) algorithm and sum-product algorithm (SPA). The proposed soft bit-flipping algorithm requires only simple comparison and addition operations for computing the messages between bit and check nodes, and the amount of those operations is also small. By increasing the utilization ratio of the computed messages and by adopting nonuniform quantization, the signal-to-noise ratio (SNR) gap to the SPA is reduced to 0.4dB at the frame error rate of 10-4 with only 5-bit assignment for quantization. LDPC codes with high column or row weights, which are not suitable for the SPA decoding due to the complexity, can be practically implemented without much worsening the error performance.

• Korean Journal of Optics and Photonics
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• v.17 no.2
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• pp.181-185
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• 2006

A novel 60GHz optical carrier generator with a polarization domain-inverted structure is suggested and is demonstrated. The two arms of the Mach-Zehnder optical waveguide are periodically poled for quasi-phase velocity matching between the optical wave at 1550nm and the RF wave at 30 GHz. The center frequency of band-pass modulation and the 3 dB bandwidth of the fabricated modulator were measured to be 30.3 GHz and 5.1 GHz, respectively. Sub-carriers with the frequency difference of 60GHz waeregenerated under appropriate DC biac voltage application while the carrier was suppressed to lead to the power ratio between the modulated sub-carrier and the suppressed fundamental carrier of 28 dB, which proves that double sideband- suppressed carrier(DSB-SC) operation can be realized by the suggested single device.

• Journal of radiological science and technology
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• v.43 no.2
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• pp.65-70
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• 2020

PA(postero-anterior) and AP(antero-posterior) chest projections are the most sought-after types of all kinds of projections. But if a radiological technologist puts wrong information about the position in the computer, the orientation of left and right side of an image would be reversed. In order to solve this problem, we utilized CNN(convolutional neural network) which has recently utilized a lot for studies of medical imaging technology and rule-based system. 70% of 111,622 chest images were used for training, 20% of them were used for testing and 10% of them were used for validation set in the CNN experiment. The same amount of images which were used for testing in the CNN experiment were used in rule-based system. Python 3.7 version and Tensorflow r1.14 were utilized for data environment. As a result, rule-based system had 66% accuracy on evaluating whether the orientation reversal on chest x-ray image. But the CNN had 97.9% accuracy on that. Being overcome limitations by CNN which had been shown on rule-based system and shown the high accuracy can be considered as a meaningful result. If some problems which can occur for tasks of the radiological technologist can be separated by utilizing CNN, It can contribute a lot to optimize workflow.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.6 s.121
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• pp.620-628
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• 2007

An H-sector horn antenna has a constant beam coverage characteristic and it can be useful for application to a wide band phased array antenna system. In this paper, we designed a broadband E-plane H-sector horn phased-array antenna, which has a 3:1 bandwidth and ${\pm}60^{\circ}$ beam steering capability. An H-sector hem antenna was designed to have $30{\sim}50^{\circ}$ half-power beam width in the principal H-plane. The active reflection coefficient including mutual coupling was calculated using a waveguide simulator, and the active reflection characteristic was improved by mutual coupling over wide frequency range. Using these results, an $8{\times}1$ H-sector phased array antenna was fabricated. The measurement results for the half-power beam width in the principal H-plane and the active reflection coefficient showed a good agreement with the simulation results. The peak-value pattern in the steered radiation beams also agreed well with the active element pattern. The measured active reflection coefficients within the beam steering range are mostly less than 0.3 over the 3:1 frequency range.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.5
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• pp.640-645
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• 2012

DC-DC converter and DC-AC inverter in a hybrid electric vehicle (HEV) generate the switching noise. It may be generated by the reverse recovery operation of the power diode in the switching circuit of the converter or the inverter. The shape of the reverse recovery region may be determined by both reverse time and recovery time in the diode. So, in this paper, the frequency spectrum of switching noise was estimated by the shape of the reverse recovery region and compared with the measured results. It shows that the meaningful region of the frequency spectrum is directly related with the reverse time.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.5
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• pp.1055-1063
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• 2012

The noise of image is added by many environmental factors. Therefore, we need to remove these noises using the conventional filtering methods, which are optimized based on the statistical characteristic of noise. In direct restoration method, there is an inverse filter and the wiener filter. Here, the wiener filter is the optimized filter in the view of least square method. First, we are going to study the inverse filter, wiener filter, constraint least square filter. Second, in order to control the quantity, we use the parameters instead of the power spectrum ratio. But, these parameters have the conflicting condition, therefore, we optimized the variables using parametric wiener filter which adjust the application appropriately. In the simulation results, the contrast of the degraded image was enhanced and the noise was removed. Comparative experimentation was demonstrated edge preserving and noise removing property.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.10
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• pp.975-983
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• 2009

This paper presents the work being carried out in order to deduce hover performance of a small-scale single rotor blade as a preliminary study of a small coaxial rotor helicopter development. As an initial research, a test stand capable of measuring thrust and torque of a small-scale rotor blade in hover state was constructed and fabricated. The test stand consists of three parts; a rotating device, a load measuring sensor and a data acquisition system. Thrust and torque were measured with varying collective pitch angle at fixed RPM. Through this research, hover performance tests were conducted for a small-scale single rotor blade operating in low Reynolds number ($Re\;{\approx}3{\times}10^5$), as well as for verifying the test stand itself for acquiring hover performance.

• The Transactions of the Korea Information Processing Society
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• v.6 no.12
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• pp.3652-3661
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• 1999

To support multimedia applications such as a multimedia communication systems and multimedia broadcasting, an operating system need to predict their timing-constraints. So, In this real-time systems, we must solve the priority inversion problem that may make the behavior of unpredictable systems and need a real-time server model that provides a better preemptability and minimizes a system overhead. In current real-time systems, the single thread server model, the worker model and the dynamic server model are being used for synchronization but they cannot propose an effective structure for managing shared resources. In this paper, the priority inheritance protocol is used to solve the priority inversion problem and the hybrid prioritized worker model is proposed, which can provide a more effective structure and a faster response time minimizing a system overhead. The hybrid prioritized worker model is to combine the static and the dynamic prioritized worker model, and have a better performance than other models in response time which is an important factor in a real-time system.