• Journal of Institute of Convergence Technology
• /
• v.5 no.2
• /
• pp.27-32
• /
• 2015

Air intakes are an essential component of aircraft engines. They are mainly used to offer uniform airflows to engine faces. Fighter aircraft have to mask the engine face inside the fuselage in order to reduce the Radar Cross Section(RCS). Therefore, offset intakes like a S-Duct are one of promising components for this purpose. During a fight, it is unavoidable that the flow will enter the intakes at some face angles other than zero. In this case, the performance of the aircraft engine will be influenced to the angle of incidence. In this study, the CFD analysis of the semi-circular S-Duct with AR(0.5,0) is performed to investigate the influence of the angle of incidence on the performance of the S-Duct using a distortion coefficient. To consider the adverse pressure gradient, a $k-{\omega}$ SST turbulence model is employed. The secondary flow and flow separation are observed for all computational cases. It is found that the positive incidence angle produces the best performances.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2007.06a
• /
• pp.565-568
• /
• 2007

In this paper, we designed and fabricated a broadband probe with a double-ridged waveguide for broadband near-field measurements. An exponentially tapered ridge in the rectangular waveguide and a novel waveguide transition were used for broadband impedance matching. The probe has broadband characteristics and its measured impedance bandwidth is approximately 123% (4.17:1) in the range 12.0-50 GHz for standing wave ratios (SWR) < 3.0. The peak radiation gain range and nominal radar cross-section (RCS) are 5.7-14.3 dBi. The performance of this probe was verified using the measured results and is in good agreement with the simulated results.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.23 no.3
• /
• pp.204-212
• /
• 2020

For general target tracking works by receiving a set of measurements from sensor. However, if the SNR(Signal to Noise Ratio) is low due to small RCS(Radar Cross Section), caused by remote small targets, the target's information can be lost during signal processing. TBD(Track Before Detect) is an algorithm that performs target tracking without threshold for detection. That is, all sensor data is sent to the tracking system, which prevents the loss of the target's information by thresholding the signal intensity. On the other hand, using all sensor data inevitably leads to computational problems that can severely limit the application. In this paper, we propose an iterative Joint Integrated Probabilistic Data Association as a practical target tracking technique suitable for a low SNR multi-target environment with real time operation capability, and verify its performance through simulation studies.

• Bulletin of the Korean Space Science Society
• /
• 2010.04a
• /
• pp.28.2-28.2
• /
• 2010

영상레이더 위성으로부터 획득된 SAR 영상의 상대적/절대적 방사(radiometric) 정밀도를 만족시키기 위해서는 궤도상에서 검보정을 수행하여야 한다. 일반적으로 상대 방사 정밀도의 보정을 위해서는 아마존 일대와 같이 일정한 지표 반사도를 지니는 넓은 지역을 촬영함으로써, 지상에서 모델링된 안테나 패턴의 이상 유무를 검증한다. 절대 방사 정밀도를 결정하기 위해서는 보정계수(calibration constant)를 구해야 하는데, 이를 위해서 RCS(radar cross section) 값이 기 알려져 있는 지상의 CR(corner reflector)를 관측해야 한다. 대부분의 SAR 위성의 경우, 각 입사각별로 여러 개의 빔(beam)이 독립적으로 운용되고, 위성의 경로가 각 pass 사이 거의 일정한 간격을 가지기 때문에, 지상의 CR들에 대한 빔의 접근성이 상당히 제약을 많이 받게 된다. 즉, 개별 빔이 촬영할 수 있는 CR의 개수 및 동일 CR에 대한 촬영 빈번도가 많이 작을 수 있다는 것을 의미한다. 특히, CR이 빔폭의 중심에서 관측되어야 하는 요구사항이 추가로 반영될 경우 그 빈도수는 더욱더 영향을 받게된다. 이 연구에서는 고도 550 km, 28일의 지상반복주기(repeat ground track)를 가지는 여명 궤도(dawn-dusk orbit)를 가정하고, 각 빔별로 그 빔에 할당된 하나의 CR만을 촬영해야 된다는 조건하에, 빔 접근성의 요구사항을 최대로 만족시킬 수 있는 CR의 좌표들을 구하였다. 동시에, J2항만을 고려한 이상적 28일 지상반복궤도를 적용한 경우와 모든 중력섭동항을 적용한 최적궤도를 적용한 경우를 비교하여, 실질적 검보정 일정을 수립하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2008.03a
• /
• pp.330-339
• /
• 2008

Ground-based interceptors(GBI) comprise a major element of the strategic defense against hostile targets like Intercontinental Ballistic Missiles(ICBM) and reentry vehicles(RV) dispersed from them. An optimum design of the subsystems is required to increase the performance and reliability of these GBI. Propulsion subsystem design and optimization is the motivation for this effort. This paper describes an effort in which an entire GBI missile system, including a multi-stage solid rocket booster, is considered simultaneously in a Genetic Algorithm(GA) performance optimization process. Single goal, constrained optimization is performed. For specified payload and miss distance, time of flight, the most important component in the optimization process is the booster, for its takeoff weight, time of flight, or a combination of the two. The GBI is assumed to be a multistage missile that uses target location data provided by two ground based RF radar sensors and two low earth orbit(LEO) IR sensors. 3Dimensional model is developed for a multistage target with a boost phase acceleration profile that depends on total mass, propellant mass and the specific impulse in the gravity field. The monostatic radar cross section (RCS) data of a three stage ICBM is used. For preliminary design, GBI is assumed to have a fixed initial position from the target launch point and zero launch delay. GBI carries the Kill Vehicle(KV) to an optimal position in space to allow it to complete the intercept. The objective is to design and optimize the propulsion system for the GBI that will fulfill mission requirements and objectives. The KV weight and volume requirements are specified in the problem definition before the optimization is computed. We have considered only continuous design variables, while considering discrete variables as input. Though the number of stages should also be one of the design variables, however, in this paper it is fixed as three. The elite solution from GA is passed on to(Sequential Quadratic Programming) SQP as near optimal guess. The SQP then performs local convergence to identify the minimum mass of the GBI. The performance of the three staged GBI is validated using a ballistic missile intercept scenario modeled in Matlab/SIMULINK.

• Journal of Advanced Navigation Technology
• /
• v.20 no.2
• /
• pp.134-140
• /
• 2016

This paper analyzed flight trajectory characteristics of ballistic missiles considering effects of drag forces. It is difficult to intercept ballistic missiles which fly over atmosphere with supersonic speeds and small radar cross section (RCS). In particular, the velocities in the phases of boost and terminal are changed significantly due to the steep variation of the drag force. Therefore, in order to build up a successful ballistic missile defense systems, the effects of the drag forces should be considered in the analysis of ballistic missile trajectory characteristics. In this point of view, this work analyzed the effects of drag forces and derived the flight trajectory characteristics of Scud B, C and Nodong missiles. Model of the ballistic missile flight trajectory is considered the effects of Coriolis and centrifugal forces, and specifications of the missiles are open sources.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.25 no.3
• /
• pp.339-347
• /
• 2014

In this paper, the authors present a new design for a broad-band metamaterial(MTM) absorber that utilizes flexible substrate. The proposed MTM unit cell is constructed by a electric-inducive-capacitive(ELC) resonator and a cut-wire on the same side of the flexible polyimide substrate. To reduce the radar cross section at frequencies other than the targeted frequency bands, the metallic pattern layer of the proposed structure is placed facing toward the incident wave propagation direction. A prototype absorber was fabricated with a planar array of $33{\times}45$ unit cells. Our experiments showed that the proposed absorber exhibits a peak absorption rate of 92 % and 93 % at 9.06 GHz and 15.0 GHz, respectively, and 75 % of the full-width at half-maximum(FWHM) bandwidth is achieved. The proposed backplane-less MTM structure can be used for a broad-band microwave absorber and irregular surface applications.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.27 no.1B
• /
• pp.114-124
• /
• 2002

In this paper, we proposed the image-based 3D ray tracing indoor propagation model using a patch scattering model for fading analysis of indoor propagation environments. An image-based 3D ray tracing technique is mainly used, which allows the rapid generation of the complex channel impulse response for any given location and polarization of transmitter and receiver. Due to the site specific nature of indoor environment, we took into account the location and the electrical properties of individual walls and objects such as windows, doors and plaster board in our propagation model. Besides, the 3D radiation beam-patterns and polarizations of arbitrary antennas were considered, and using patch scattering model we can consider the change of the polarization due to the scattering from the various indoor objects, like desks, chairs and etc. the are almost impossible to be modeled with the basic image-based ray tracing method. The model will predict the impulse response, the rms delay spread, the fading characteristics of the channel and performances of the polarization diversity schemes.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.43 no.2
• /
• pp.109-117
• /
• 2015

Aircraft needs an inlet duct to supply the airflow to engine face. A fighter aircraft that requires low radar observability has to hide the engine face in the fuselage to reduce the Radar Cross Section(RCS). Therefore, the flow path of the inlet duct is changed into S-shape. The performance of the aircraft engine is known to be influenced by the shape and the centerline curvature of the S-Duct. In this study, CFD analysis of the RAE M 2129 S-Duct has been performed to investigate the influence of aspect ratio of inlet geometry. The performance of the S-Duct is evaluated in terms of the distortion coefficient. To simulate the flow under adverse pressure gradient better, $k-{\omega}SST$ turbulence model is employed. The computational results are validated with the ARA experimental data. The secondary flow and the flow separation are observed for all computational cases, while the semi-circular geometry has been found to produce the best results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.22 no.7
• /
• pp.711-719
• /
• 2011

A study of miniaturization of an L-band orthomode transducer(OMT) for field experiments of radar backscatter is presented in this paper. The proposed OMT is not required the additional waveguide taper structures to connect with a standard adaptor by the newly designed junction structure which bases on a waveguide taper. Total length of the OMT for L-band is about 1.2 ${\lambda}_o$(310 mm) and it's a size of 60 % of the existing OMTs. And, to increase the matching and isolation performances of each polarization, two conducting posts are inserted. The bandwidth of 420 MHz and the isolation level of about 40 dB are measured in the operating frequency. The L-band scatterometer consisting of the manufactured OMT, a horn-antenna and network analyzer(Agilent 8753E) was used STCT and 2DTST to analysis the measurement accuracy of radar backscatter. The full-polarimetric RCSs of test-target, 55 cm trihedral corner reflector, measured by the calibrated scatterometer have errors of -0.2 dB and 0.25 dB for vv-/hh-polarization, respectively. The effective isolation level is about 35.8 dB in the operating frequency. Then, the horn-antenna used to measure has the length of 300 mm, the aperture size of $450{\times}450\;mm^2$, and HPBWs of $29.5^{\circ}$ and $36.5^{\circ}$ on the principle E-/H-planes.