• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.5
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• pp.558-565
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• 2013

In this paper, modeling and simulation for performance analysis of high resolution SAR system has been carried out in the time, frequency and numeric domain using ADS Ptolemy simulation tool of Agilent corporation. SAR system consists of antenna, controller and transceiver. Error parameters affecting SAR system performances have been defined, modeled and simulated such as phase noise of frequency synthesizer, amplitude and phase characteristic of TWTA, sampling frequency of waveform generator and I/Q imbalance. Finally, the development requirements of SAR system based on the impulse response function have been derived.

• Proceedings of the IEEK Conference
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• 1999.11a
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• pp.143-146
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• 1999

The traditional FDTD method in the stair case, the CP-FDTD method, the modified CP-FDTD method, and Dey method have been developed to analyze smooth-curved- surface structures. These methods have some disadvantages such as inaccuracy of the stair-case FDTD, instability of the modified CP-FDTD, and complexity of Dey method. The improved algorithm presented here is a mixed-form of the modified CP algorithm and Dey algorithm. It is to avoid collinear borrowing approximations and to manipulate field update equations. All of preceding methods are applied to the E-plane sectoral horn antenna to get far-field patterns. The validity and applicability of the presented one is to be shown by comparing computed far-field patterns with measured values.

• Proceedings of the IEEK Conference
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• summer
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• pp.339-342
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• 2004

In this paper, we investigated methods to reduce SAR(Specific Absorption Rate) value with EMI(Electromagnetic Interference) paint distribution on front case of mobile handset. Simulations for several different EMI patterns were carried out. For the purpose of modeling, we used 3 dimensional CAD(Computer Aided Design) program, `Pro-engineering'. SAR simulation was done with SEMCAD, simulation platform for electromagnetic compatibility antenna design and dosimetry. In order to distinguish the individual pieces and to enable an assignment of the different material properties, each subfile was imported separately. In simulation, folding angle was set to $142^{\circ}.$ If we vary folding angle, different SAR value will be obtained. Among the tested EMI paint patterns, the hairpin pattern showed the best performance, i.e. the decrease efficiency of $16.5\%$ and horizontal-direction zigzag pattern showed the decrease efficiency of $12.2\%$ when we set the completely removed pattern as reference.

• Journal of electromagnetic engineering and science
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• v.10 no.4
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• pp.219-223
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• 2010

Based on a provided closed-form wireless power transmission (WPT) efficiency formula, which may be used for any value of load, we have analyzed the WPT efficiencies between two metamaterial-inspired loop antennas in various aspects. Due to the modeling based on low frequency circuit theory, the provided formula at the center resonant frequency has been found to be accurate until when the distance between the two loop antennas increases to 15 cm (about $\lambda_0/6$ at 300 MHz). When the two loops get closer, the resonant frequency has been found to split into two in theory, simulations, and measurements. The EM-simulated and measured efficiencies at new resonant frequencies are 60.9 % and 46.3 %, respectively, at d=15 cm. With two extra rings around the loops, the maximum efficiency is enhanced to 93.7 % at d=15 cm. The effect of the additional two rings is about 30 %.

• Journal of the Korea Institute of Military Science and Technology
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• v.2 no.2
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• pp.226-233
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• 1999

A transmitting antenna mounted on the naval vessels can be easily exited by exogenous disturbances such as wave and impact. Gimbal system need for the controller to maintain the robust performance against various modeling uncertainties and disturbances. PI controller, however, cannot supply good robust performance under situation. Thus a robust $H_{\infty}$ control scheme is used to ensure a specified dynamic response under above conditions. Gimbal system controlled simplified as 2 DOF system that ignored coordinate co-relations of each direction and hydraulic system is linearly modelled. In this paper, we compared those of simulation to the results of experiment and H$_{\infty}$ controller, proposed, showed the good response and stability than PI controller.

• Journal of KIISE:Software and Applications
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• v.26 no.10
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• pp.1143-1155
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• 1999

셀룰러 방식의 이동통신 시스템에서 전파의 유효신호 도달범위를 예측하기 위해서는 전파전파 모델을 이용한 예측기법이 주로 사용된다. 그러나, 전파과정에서 주변 지형지물에 의해 발생하는 전파손실은 매우 복잡한 비선형적인 특성을 가지며 수식으로는 정확한 표현이 불가능하다. 본 논문에서는 신경회로망의 함수 근사화 능력을 이용하여 전파손실 예측모델을 생성하는 방법을 제안한다. 즉, 전파손실을 송수신 안테나간의 거리, 송신안테나의 특성, 장애물 투과영향, 회절특성, 도로, 수면에 의한 영향 등과 같은 전파환경 변수들의 함수로 가정하고, 신경회로망 학습을 통하여 함수를 근사화한다. 전파환경 변수들이 신경회로망 입력으로 사용되기 위해서는 3차원 지형도와 벡터지도를 이용하여 전파의 반사, 회절, 산란 등의 물리적인 특성이 고려된 특징 추출을 통해 정량적인 수치들을 계산한다. 이와 같이 얻어진 훈련데이타를 이용한 신경회로망 학습을 통해 전파손실 모델을 완성한다. 이 모델을 이용하여 서울 도심 지역의 실제 서비스 환경에 대한 타 모델과의 비교실험결과를 통해 제안하는 모델의 우수성을 보인다.Abstract In cellular mobile communication systems, wave propagation models are used in most cases to predict cell coverage. The amount of propagation loss induced by the obstacles in the propagation path, however, is a highly non-linear function, which cannot be easily represented mathematically. In this paper, we introduce the method of producing propagation loss prediction models by function approximation using neural networks. In this method, we assume the propagation loss is a function of the relevant parameters such as the distance from the base station antenna, the specification of the transmitter antenna, obstacle profile, diffraction effect, road, and water effect. The values of these parameters are produced from the field measurement data, 3D digital terrain maps, and vector maps as its inputs by a feature extraction process, which takes into account the physical characteristics of electromagnetic waves such as reflection, diffraction and scattering. The values produced are used as the input to the neural network, which are then trained to become the propagation loss prediction model. In the experimental study, we obtain a considerable amount of improvement over COST-231 model in the prediction accuracy using this model.

• Journal of Korea Society of Industrial Information Systems
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• v.20 no.5
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• pp.1-11
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• 2015

This paper is focused on how the trajectory of launch vehicle could be optimally estimated by the quadratic regression of trajectory data mining for the operation of telemetry ground system in NARO space center during real-time. To receive the telemetry data, the telemetry ground system has to track the space launch vehicle without tracking loss, and it is possible by the well-designed algorithm to estimate a flight position in real-time. For this reason, the quadratic regression model instead of interpolation was considered to estimate the exact position data of launch vehicle and the improvement of antenna performance. For analysis, the real trajectory data which had been logged during NARO 1st launch mission were used, the estimation result of launcher current position was analyzed by the mathematical modeling. In conclusion, the algorithm using quadratic regression based on trajectory data mining showed the better performance than previous interpolation algorithm to estimate the next flight position and the antenna driving performance.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.3
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• pp.409-426
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• 2001

Absorbed power of the human head radiated from a 900 MHz portable phone and temperature rise are computed using FDTD(Finite-Difference Time-Domain) method. For this computation the 5 layered media for the human head modeling and the monopole antenna attached to metallic box for the portable phone are used. To reflect the real circumstances typical sizes of human heads and portable phones are considered in the calculation. The length of monopole antenna is 8.15 cm, and the output power of a phone is 600 mW. Under the predetermined model the distribution of 1 g, 10 g averaged SAR and temperature rise rate over the human head are calculated, from which it was found that the position of maximum SAR is near at the head skin surface, not deep places far into the head. The position of the highest temperature is located far from the head skin more than that of the maximum SAR occured. The averaged SAR and temperature along the distance between the head and phone are calculated according to seperation distance between the head and phone.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.4
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• pp.491-498
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• 1998

Based on FDTD(Finite-Difference Time-Domain) method the human head absorbed power radiated from a 1.8 GHz portable phone is computed. For this computation the 7 layered media for the human head modeling and the monopole antenna attached to metallic box for the portable phone are used. To reflect the real circumstances typical sizes of human heads and portable phones are considered in the calculation. The length of monopole antenna is 4.5 cm. Under the predetermined model the distribution of SAR over the human head are calculated, and from which the place of maximum SAR is near the head skin surface, not deep places far into the head. The computation shows the maximum SAR to be 1.4 mWg somewhat less than the internationally adopted value of 1.6 mW/g.

• Journal of Satellite, Information and Communications
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• v.9 no.2
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• pp.74-79
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• 2014

Conventional ScanSAR mode has been adopted in Envisat or Radarsat and played an important role to acquire wide swath SAR images for environmental surveillance. However, it suffers from the undesirable scalloping effect caused by non-homogeneity of antenna pattern while the image resolution is sacrificed. In recent years, TOPS mode has been suggested and put into use to overcome the disadvantages of the conventional scanning mode. Although TOPS mode is able to produce wide-swath SAR image in a short time interval, it demands highly complicated system design knowledge. In this paper, we present the operation principle of TOPS mode and a full SAR simulation is performed to generate TOPS SAR raw data. Azimuth antenna pattern is modified during TOPS mode operation and it is shown that the undesired scalloping effect is suppressed in the generated SAR image.