Noh-Hoon Myung

A deterministic ray tube method for microcellular wave propagation prediction model

In this paper, we present a new and very fast ray-tracing method using a ray tube tree, which is based on uniform geometrical theory of diffraction (UTD) and can solve some of the problems that other ray-tracing methods have. It is developed for quasi three-dimensional (3-D) environments and can be applied to any complex propagation environment composed of arbitrary-shaped buildings and streets. It finds all propagation paths from a transmitter to a receiver extensively with very high computation efficiency. It is fundamentally a point-to-point tracing method, so reception tests are not required and it guarantees high accuracy. To validate our ray-tracing method, signal path loss and root mean square (rms) delay spread were computed in the downtown core of Ottawa, Canada, and they were also compared with the published measurements. The results of the proposed method in this paper show good agreement with the measurements. The computation time required to obtain a path loss map in the site is revealed to be very short in comparison with other methods.

Locally tensor conformal FDTD method for modeling arbitrary dielectric surfaces

This paper introduces a new effectie finite-difference () time-domain FDTD algorithm for modeling arbitrarily shaped dielectric surfaces. The new algorithm is based on an effectie medium theory that makes the dielectric tensor effectie. The proposed FDTD analysis of TE () scattering by rotated two-dimensional 2-D dielectric cylinders proides excellent numerical results. Q 1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 23: 245)249, 1999.

Azimuth Beam Pattern Synthesis for Airborne SAR System Optimization

The limitation of the pulse repetition frequency (PRF) of an airborne synthetic aperture radar (SAR) system is not a serious problem to obtain high azimuth resolution and wide swath imaging compared with a spaceborne SAR system. Hence, continuous high azimuth resolution imagery over a wide area can be obtained using an antenna having a wide beamwidth. Since a small antenna with a large beamwidth has very low gain, which results in di-culty in detection; the azimuth beam pattern optimization of a large active phased array antenna is needed for airborne SAR system optimization. To improve the airborne SAR system performance, such as the noise- equivalent sigma zero (NEae0), the azimuth resolution, the radiometric accuracy (RA), and the azimuth ambiguity ratio (AAR), we present an optimal azimuth beam pattern mask template and suggest an azimuth beam pattern satisfying the mask template using the particle swarm optimization (PSO). The mode having the proposed beam pattern guarantees continuous and high resolution images, simultaneously.

Simple K-band MMIC VCO utilizing a miniaturized hairpin resonator and a three-terminal p-HEMT varactor with low phase noise and high output power properties

Presents a fully monolithic K-band MMIC voltage-controlled oscillator (VCO) implemented by using a 0.25 /spl mu/m AlGaAs/InGaAs pseudomorphic HEMT (p-HEMT) technology. The use of a half-wavelength miniaturized hairpin-shaped resonator and a three-terminal p-HEMT varactor was effective in reducing the chip size and simplifying fabrication processes of the microwave MMIC VCO without impairing the performance of the circuit. The VCO provides a typical output power of 11.5 dBm at 20.8 GHz and a free-running phase noise of -82 dBc/Hz at 100 kHz offset and -95 dBc/Hz at 1 MHz offset. It also shows a tuning range of 70 MHz with little reduction in output power and high yield properties. The chip size of the MMIC VCO is 1.5 /spl times/ 2.0 mm/sup 2/.

TM scattering from hollow and dielectric-filled semielliptic channels with arbitrary eccentricity in a perfectly conducting plane

The behavior of TM wave scattering from hollow and dielectric-filled semielliptic channels in a perfectly conducting substrate is investigated. The scattered field is represented in terms of an infinite series of Mathieu functions with unknown coefficients. By applying the separation of variables and employing the partial orthogonality of the first-kind angular Mathieu functions, the unknown coefficients are obtained. Numerical results are given for the scattered-field patterns by the channels with different eccentricities and permittivities.

Scattering Analysis of Open-Ended Cavity with Inner Object

Scattering from a concave structure, such as an open-ended cavity, which is electrically long and has an abruptly varying curved surface or an inner scattering object has been analyzed by the hybrid method integrating the HF and LF methods. In this paper the interfacing procedures of the SBR-FDTD method and the iterative PO-FDTD method were presented and the two methods to determine the iteration number of IPO simulation were proposed and verified by the comparison with that of mode analysis.

A NOVEL HYBRID AIPO-MOM TECHNIQUE FOR JET ENGINE MODULATION ANALYSIS

A novel hybrid adaptive iterative physical optics- method of moments (AIPO-MoM) technique is presented for the electromagnetic analysis of jet engine structures that are both electrically large and complex in both stationary and dynamic cases. In this technique, the AIPO method is used to analyze the smooth inlet region, and the MoM method is used to analyze the electrically complex compressor region, including blades and a hub. It is e-cient and accurate by virtue of combining the respective merits of both methods. In the dynamic case, a concept for modifled impedance equation is proposed to reduce computational load. Numerical results are presented and verifled through comparison with Mode-FDTD and measured and commercial simulation packages results.

Radar Cross Section Measurements of a Realistic Jet Engine Structure with Rotating Parts

Radar cross section (RCS) data are measured from a realistic aircraft jet engine structure with rotating parts, and the characteristics are analyzed. The model has an inlet with dimensions of 0.866 m × 0.866 m × 0.703 m, 35 degree skewed three stage rotor blades attached to the rotating shaft with a motor, and the number of blades are 17, 29, and 41. The experimental results show that the jet engine modulation (JEM) patterns are very complicated and can be used to extract meaningful distinct features.

Joint Time-Frequency Analysis of Radar Micro-Doppler Signatures from Aircraft Engine Models

Micro-Doppler signatures from four CAD aircraft engine models and one experimental engine model are analyzed using joint time-frequency analysis (JTFA). The signatures are obtained from shooting and bouncing rays (SBR) simulation for the CAD models and from measurement for the experimental model. The JTFA results give additional useful physical feature information regarding the respective engines, such as whether the number of blades is odd or even and the length of blades, in addition to the number of blades, which can be extracted by traditional spectrum analysis.

MODIFIED HILBERT-HUANG TRANSFORM AND ITS APPLICATION TO MEASURED MICRO DOPPLER SIGNATURES FROM REALISTIC JET ENGINE MODELS

Joint time-frequency analysis (JTFA) is applied to micro Doppler signatures generated by jet engine modulation (JEM) efiect using a modifled Hilbert-Huang transform (HHT). The modifled HHT is developed to improve the JTFA results of measured JEM signals. Wavelet decomposition (WD) with Meyer wavelet function is considered as a supplementary process of the HHT. The modifled HHT examines a signature obtained from simulation of a jet engine CAD model, and is then applied to the signatures obtained from measurement of two realistic jet engine models. The modifled HHT gives more improved JTFA results of the measured JEM signals than those from the simple short-time Fourier transform | (STFT) based analysis. The modifled HHT-based JTFA approach is expected to be signiflcantly useful for enabling high-quality radar target recognition in a real environment by complementing other traditional analyses.