• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.130-134
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• 1996

본 논문에서는 광대역 소음원의 위치를 탐지하여 2차원 영상면에 소음원을 영상화할 수 있는 3차원 마이크로폰 배열을 제안하였다. 배열요소간의 상호상관함수가 2차원 영상면의 화소의 밝기에 대응되도록 영상함수를 유도하였으며 영상면은 사각면 및 원통면등으로 선택 가능 하도록 하여 소음원의 위치동정 해석이 용이하도록 하였다. 몇가지 소음원에 대한 수치 모의 실험결과는 제안된 배열이 소음제어 분야 등에 응용 될 수 있음을 보인다.

• The Journal of the Acoustical Society of Korea
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• v.20 no.2
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• pp.86-92
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• 2001

Various array processing techniques to identify the noise source position or bearing have been developed. Typical array processing techniques which are based on time delay between received signals at two sensors, are classified as conventional beamforming, correlation function and NAH (Near-Field Acoustic Holography) techniques which have their own characteristics with respect to application field and signal processing method. In this study, correlation function technique which could be applied for broadband noise source detection, is adopted and the effective detection technique is proposed considering the effects of source bandwidth and measurement noise correlation of noise sources. The validity of the Proposed technique is evaluated using the 3-dimensional nonlinear any which does not give 3-dimensional Position or bearing ambiguity

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.6
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• pp.1123-1129
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• 2003

The noise of maneuvering submarines or vessels can be divided into the tonal signals and broadband ambient noise. Tonal signals are from the revolution of motors and engines of vessels, and broadband ambient noise is from the bubbles which are generated by the propellers and the flow of water around vessels. We can analyze the kinds and the speed of vessels if we analyze the tonal signals and ambient noise. But, it is difficult to divide the tonal signals form the ambient noise when the power of tonal signal is much weaker than the power of ambient noise. In this paper, we detect the direction of arrival(DOA) of the noises generated by vessels with the automatic tracking window(ATW) preprocessing algorithm, and make a beam to the direction of the targets. We suggest a method which can separate weak tonal signals from broadband ambient noise with the ATW algorithm.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.1
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• pp.36-46
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• 2013

This paper proposes the design of broadband spiral antenna for a potable non-linear junction detector (NLJD) system. To realize the broadband antenna design, it was considered optimization of the number of spiral turns by iteration calculation. Ground plane with the Archimedean spiral slit to keep the same current distribution between radiating plane and ground is considered for circular polarization design. In order to realize high directivity and high gain of the proposed antenna, the cavity wall and the metal cap which is located on back of ground plane were also considered in design. Measurement results of return loss were agreed well with VSWR 2:1 at interested frequency band among 2.4 to 2.44 GHz, 4.84 to 4.92 GHz and 7.28 to 7.36 GHz. Measured axial ratio was observed 3 dB below and showed reasonable agreement with simulation results. Characteristics of the RHCP(Right Hand Circular Polarization) with the measured gain of 6.8 dBi above at interested frequency band were also observed.

• The Journal of the Acoustical Society of Korea
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• v.38 no.3
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• pp.256-265
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• 2019

Several types of cymbal transducers used for underwater detection have been studied. Representative types are Moonie, convex cymbal, and concave cymbal transducers. In this study, we analyzed the characteristics of these three types of transducers for underwater broadband projectors and compared them together. First, the influence of structural variables on the acoustic characteristics of the transducers was analyzed. Based on this, we derived the structure of each transducer type to have a specific center frequency and the maximum bandwidth. As a result of comparing the performance of the optimized transducers, the convex cymbal transducer turned out to be best in terms of both broad bandwidth and high power.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.5A
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• pp.519-527
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• 2010

In this paper, we design and implement a broadband LNA(Low Noise Amplifier), a mixer, and oscillators in RF module part for radar detector. For resolving the limitation of the conventional product that the sensitivity is low due to the poor gain flatness, we propose the architecture of RF module part. The proposed RF module part is composed with a broadband 2-stage LNA, a mixer, and three oscillators, and improves the maximum gain and gain flatness for detecting various frequencies. The overall performances of RF module part are above 38 dB conversion gain in whole band and 1 dB gain flatness. These results show that the maximum gain which is the problem of the conventional product is improved 6 dB from 35 dB to 41 dB, and gain flatness is also improved 17 dB from 22 dB to 5 dB.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.11
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• pp.3104-3109
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• 2009

The technology of direction finding is very important to find the direction of emitters for ELINT(electronic intelligence) system. The principle of TDOA(time difference of arrival) is to receive an emitter signal with two antennas, measure the time difference between two antennas, and converse the time difference to direction difference. This technology can be used in broadband frequency system and make the system very simple because a phase-discriminator and a voltage comparator are not needed. For fine DF accuracy, high time resolution receiver and long basis line antennas are needed. The DF accuracy of noise added signals is simulated with different time

• The Journal of the Acoustical Society of Korea
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• v.29 no.1
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• pp.10-17
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• 2010

In a passive sonar, the improvement of detection performance by using noise cancellation is usually a important problem. In this paper, we have analyzed the own-ship noise cancellation in the two operation modes which are used in the HMS system. In the operator mode, an adaptive line enhancer(ALE) is applied to improve the tonal detection by using broadband noise cancellation and the normalized least mean square(NLMS) algorithm is applied to the design of an adaptive filter. The reference input that is correlated with a primary input can be used to remove the noise incident on the observation directionin the automatic mode. Computer simulations with real sea that data show that the proposed adaptive noise canceller has good performance in passive detection under HMS operation.

• Proceedings of the Acoustical Society of Korea Conference
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• 1993.06a
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• pp.222-225
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• 1993

일반적임 빔 형성기는 표적의 방위탐지가 가능하지만, 구조적인 특성상 대칭적인 빔을 형성하므로 표적의 좌/우 방위 구분이 불가능하기 때문에 표적의 정확한 방위를 탐지하고자 할 때 좌/우 구분이 가능한 빔 형성기가 필수적이다. 좌/우 분리 빔 형성 기법으로는 카디오이드(Cardioid) 빔 형성기법을 일반적인 빔 형성기에 적용시키는 방법이 최적으로 알려져 왔다. 그러나 좌/우 분리 빔을 형성하기 위해서는 많은 연산량과 하드웨어 설계에 대한 고려가 있어야한다. 본 논문에서는 좌/우 분리 빔 형성을 위하여 주파수 빔 형성기법과 카디오이드 빔 형성기법을 합성하여 적용하였다. 주파수 빔 형성 기법은 짧은 수행시간 동안에 표적의 정보추출을 위하여 고려되었으며, 카디오이드 빔 형성기법은 3개의 센서를 이용하여 센서의 기울기를 보상하여 수행하는 기법을 적용하였다. 또한 방향성 있는 시뮬레이션 신호를 생성하여 좌/우 분리 빔 형성 시뮬레이션을 수행하였다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.10
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• pp.783-790
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• 2018

The frequency-hopping technique is one of the spread-spectrum techniques. Frequency hopping is a communication system in which the carrier frequency channel is hopped within the wideband. Therefore, a frequency-hopping system has such advantages as antijamming and low probability of intercept. This system is often used in military communications. Because frequency-hopping signal detection is difficult, it is an important research issue. A novel detection technique is proposed that can improve detection probability. When the received signal is transformed to a frequency domain sample by fast Fourier transform, spectral leakage lowers the detection probability. This problem can be solved by using the Hamming window, and the detection probability can be increased. However, in a frequency-hopping environment, the windowing technique lowers the detection probability. The proposed method solves this weakness. The simulation results show that the proposed detection technique improves the detection probability by as much as 13 %.