• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.12
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• pp.1321-1328
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• 2003

In this paper, we demonstrate that the directivity of the CPW(Coplanar Waveguide) directional coupler with finite-extent backed conductor is enhanced by eliminating center region of backed conductor appropriately. If the backed conductor is removed at center region of couplers, the couplers have two backed conductors. If effective odd mode dielectric constant is decreased at center region, the electrical length for odd mode is changed and phase velocity is same at the directional couplers. Hence, directivity is improved. The eliminated length is solved by an odd and even mode analysis. The designed moderate CPW directional coupler with the proposed compensation structure has excellent directivity and matching characteristic at center frequency in simulation and measurement.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.81-85
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• 2012

In this paper, the typical combustion instabilities in hybrid rocket were studied. To induce combustion instabilities in the combustor with the diaphragms were mounted, on front and rear of the fuel, and combustion experiments were performed. The calculated theoretical frequencies using Longitudinal Acoustic Mode and Helmholtz Mode are compared with experimental frequencies using FFT analysis. The theoretical calculated results showed good agreements with experimental results are compared.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.17-20
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• 2007

Effect of radial position of half-wave resonator is investigated experimentally for acoustic damping of tangential mode in a combustion chamber by adopting acoustic cold test. When resonator with optimal tuning length is installed， damping is enhanced as its radial location is away from the center of the faceplate. And, radial profile of damping factor is similar to that of the amplitude of the acoustic mode to be damped. As the location is close to the center, acoustic damping is mitigated and independent on the resonator length. on the other hand， the resonator with non-optimal length dose not show any effect of its radial position.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.8
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• pp.1108-1116
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• 1993

Y-branch directional coupler optica1 switches with two different coupling lengths are fabricated on z-cut LiNbO3 and tested at r = 1.3 rm. The normal mode and coupled mode theories are utilized to calculate device coupling length and switching voltage. Simulation of the beam propagation method (BPM) is also performed to confirm the device coupling lengths. For dc operation, experimental results are in good agreement with the modee theories expectation.

• Korean Journal of Optics and Photonics
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• v.15 no.4
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• pp.293-298
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• 2004

We investigate the effect of the wing width and thickness of a Double-Sided Deep-Ridge(DSDR) vertical directional coupler on the coupling length dependent on the polarization, We have found that the DSDR vertical directional coupler without a wing does not have polarization independent coupling lengths. The variation of the coupling length of TE and TM modes and the difference between the coupling lengths of the two modes are negligible as the wing width increases beyond the specific wing width for the same wing thickness. Thus, we can see that a DSDR vertical directional coupler has a wing width larger than the minimum wing width to obtain the polarization independent coupling length. The minimum wing width increases as the wing thickness increases for the same core thickness and as the core thickness decreases for the same wing width. Also, we have found that the minimum wing thickness is determined by the core thickness and the minimum wing thickness decreases as the core thickness increases.

• Korean Journal of Optics and Photonics
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• v.18 no.5
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• pp.295-302
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• 2007

This paper presents a rigorous comparison of the design characteristics of polarization-insensitive directional coupler (DC) and multimode interference (MMI) coupler based on rib type waveguides, by using longitudinal modal transmission-line theory (L-MTLT). It shows that the multimode mixing and interference property of MMI can be structurally designed through the continuous evolution of the two-mode coupling property of DC. It also compares and analyzes the coupling efficiency along with the coupling length and the wavelength between polarization-insensitive DC and MMI. From the design properties obtained, it demonstrates for the first time the integration of polarization-insensitive DC or MMI with a Bragg grating and evaluates precisely the filtering characteristics. The numerical results reveal that the DC, as long as it is designed to have the same coupling length for TE and TM modes, has better performance than the MMI in polarization-insensitive filtering behaviour. However, it shows that the MMI with much less coupling length than DC is preferred in the miniaturization of integrated devices.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.11a
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• pp.12-12
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• 1997

여러 가지 형태의 연소 불안정성 중에서 50-500Hz 사이에서 발생되며 길이방향 모드(longitudinal mode)로 특징이 있는 저주파수 불안정성이 램제트 혹은 재연소기(Afterburner)의 연소 불안정성에서 가장 중요한 것이라고 여겨진다. 본 논문에서는 램제트 흑은 재연소기에서 일어날 수 있는 길이 방향의 연소 불안정성을 Modal 해석법을 사용하여 수학적인 모델로 만들었다. 특히 이 모델의 선형형태는 어떤 형태든지 선형 속도에 민감한 Burning rate 모델을 사용할 수가 있어서 보다 포괄적인 형태로 만들어져 있으며, 이 모델을 이용하여 여러 가지 연소 형상과 불완전 연소 응답 등을 연구할 수 있다. 본 논문에서는 실제 연소 형상과 유사한 삼각형 모양의 연소 형상을 사용하여 기존의 다른 모델들과 비교 분석하였다.

• Journal of the Korean Society of Propulsion Engineers
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• v.12 no.2
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• pp.1-7
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• 2008

Effect of radial position of half-wave resonator is investigated experimentally for acoustic damping in a combustion chamber by adopting acoustic cold test. Acoustic damping is quantified by damping factor. When resonator with optimal tuning length is installed, damping is enhanced as its radial location is away from the center of the faceplate. And, spatial profile of damping factor is similar to that of the amplitude of the acoustic mode to be damped. As the location is close to the center, acoustic damping is mitigated and independent of the resonator length. On the other hand, the resonator with non-optimal length dose not show any effects of its radial position. Acoustic-damping capacity can be evaluated as functions of resonator length and position.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.3
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• pp.171-176
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• 2014

The polarization characteristics of ultracompact polarization-insensitive directional coupler (PIDC) based on double sandwiched rib-type waveguide are explored in detail by using longitudinal modal transmission-line theory (L-MTLT). To obtain the polarization-insensitive condition of ultracompact directional coupler, the coupling length and coupling efficiency as functions of the refractive index and thickness of sandwiched rib-type waveguide are analyzed for quasi-TE and quasi-TM modes. The numerical results show that the ultracompact polarization-insensitive coupler with hundreds of micrometer scales is realized by properly choosing structural and material parameters of double sandwiched layers. Furthermore, the influence of fundamental mode profile, which is distributed in lateral waveguide of coupler, on the coupler performance has been investigated.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.05a
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• pp.177-180
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• 2009

A Possibility of combustion instability on longitudinal mode has a high level at large scale of L/D. Solid propellant has a metal particle and a grain of control to pressure oscillation. Solid rocket motor in slotted-tube grain controls pressure oscillation of longitudinal mode. If slot length is shot, pressure oscillation of longitudinal mode is amplified by cylinder part after middle phase of total burn time. A study has analyzed pressure oscillation of longitudinal mode at spectrum and acoustic modal analysis at pressure of result on static firing test.