• Title/Summary/Keyword: 초저주파 대역

Search Result 4, Processing Time 0.02 seconds

An Experiment on Reduction of Infrasonic Underwater Self-Noise (초저주파 대역 수중 자체소음 저감에 관한 실험 연구)

  • Lee, Seong-Wook;Lee, Yong-Kuk;Kim, Seong-Ryul
    • The Journal of the Acoustical Society of Korea
    • /
    • v.30 no.1
    • /
    • pp.17-21
    • /
    • 2011
  • The effects of screening hydrophones with open-cell foams for reduction of the infrasonic self-noise induced by the flow around hydrophones are investigated by at-sea experiment. Test results of the 10 ppi polyurethane open-cell foams with different thickness show that the foams of 1 cm and 3 cm thickness reduce the flow-induced self-noises up to 20 dB and 28 dB at the frequency band of 2-10 Hz, respectively.

Ultra Low Noise Hybrid Frequency Synthesizer for High Performance Radar System (고성능 레이다용 저잡음 하이브리드 주파수합성기 설계 및 제작)

  • Kim, Dong-Sik;Kim, Jong-Pil;Lee, Ju-Young;Kang, Yeon Duk;Kim, Sun-Ju
    • Journal of the Korean Society for Aeronautical & Space Sciences
    • /
    • v.48 no.1
    • /
    • pp.73-79
    • /
    • 2020
  • Modern radar system requires high spectral purity and low phase noise characteristics for very low RCS target detection and high resolution SAR (Synthetic Aperture Radar) image. This paper presents a new X-band high stable frequency synthesizer for high performance radar system, which combines DAS (Direct Analog Synthesizer) and DDS (Direct Digital Synthesizer) techniques, in order to cope with very low phase noise and high frequency agility requirements. This synthesizer offers more than 10% operating bandwidth in X-band frequency and fast agile time lower than 1 usec. Also, the phase noise at 10kHz offset is lower than -136dBc/Hz, which shows an improvement of more than 10dB compared to the current state of art frequency synthesizer. This architecture can be applied to L-band and C-band application as well. This frequency synthesizer is able to used in modern AESA (Active Electronically Scanned Array) radar system and high resolution SAR application.

Low Frequency Characteristic of Seoul Subway Noise (서울지하철의 저주파소음 특성)

  • Jung, Sung-Soo;Shin, Su-Hyun;Kim, Ho-Chul;Lee, Woo-Seop
    • Journal of Korean Society of Environmental Engineers
    • /
    • v.27 no.11
    • /
    • pp.1193-1197
    • /
    • 2005
  • The low frequency noise below 200 Hz, including inaudible infra-sound, is known to affect human physiology ; circulation, respiration, nerve, endocrine, etc. Legislation has been introduced in several countries regarding evaluation guideline and measurement method of low frequency noise. In this work, low frequency characteristics of the Seoul subway transportation system was investigated in terms of the noise level and spectrum in the interior of running passenger car and the subway station. The interior sound pressure level of the passenger car was between 60 and 105 dB in the frequency range of $1{\sim}200\;Hz$ and varied with car speed. The marked sound pressure level peak at 8 Hz, infra-sound, observed for the most of Lines is shown to correspond to the resonance frequency of passenger car. The level of station platform noise was lower than the interior noise of running car because of the lower speed at arriving/departure. The results indicated that the interior noise level of running passenger car was inside the oppressive feeling region, proposed by Ochiai, in the frequency range of $20{\sim}80\;Hz$ which makes a little concern.

A 30 GHz Band Low Noise for Satellite Communications Payload using MMIC Circuits (MMIC 회로를 이용한 위성중계기용 30GHz대 저잡음증폭기 모듈 개발)

  • 염인복;김정환
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
    • /
    • v.11 no.5
    • /
    • pp.796-805
    • /
    • 2000
  • A 30GHz band low noise amplifier module, which has linear gain of 30dB and noise figure of 2.6dB, for 30GHz satellite communication transponder was developed by use of MMIC and thin film MIC technologies. Two kinds of MMIC circuits were used for the low noise amplifier module, the first one is ultra low noise MMIC circuit and the other is wideband and high gain MMIC circuit. The pHEMT technology with 0.15$mu extrm{m}$ of gate length was applied for MMIC fabrication. Thin film microstrip lines on alumina substrate were used to interconnect two MMIC chips, and the thick film bias circuit board were developed to provide the stabilized DC bias. The input interface of the low noise amplifier module was designed with waveguide type to receive the signal from antenna directly, and the output port was adopted with K-type coaxial connector for interface with the frequency converter module behind the low noise amplifier module. Space qualified manufacturing processes were applied to manufacture and assemble the low noise amplifier module, and space qualification level of environment tests including thermal and vibration test were performed for it. The developed low noise amplifier was measured to show 30dB of minimum gain, $\pm$0.3dB of gain flatness, and 2.6dB of maximum noise figure over the desired operating frequency range from 30 to 31 GHz.

  • PDF