Ho Lim

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.

HIGH RESOLUTION RANGE PROFILE-JET ENGINE MODULATION ANALYSIS OF AIRCRAFT MODELS

This paper presents an analysis of high resolution range profile-jet engine modulation (HRRP-JEM) signatures of aircraft models. Two types of aircraft models are designed, and radar cross section (RCS) data is collected using a shooting and bouncing rays (SBR) technique. Then HRRP-JEM signatures are acquired using a two-stage Fourier transform-based signal process. For the radar target identification, the location information is estimated by an engine location extraction algorithm. The analysis results show that the estimation of the location information of the engine could be useful for radar target identification.

Analysis and design of a UHF RFID tag antenna with a Split Ring Resonator

In this paper, the UHF RFID tag antenna which has a SRR as a radiating part and inductively coupled feeding method are analyzed and designed. By using a SRR, the antenna size can be reduced and using an inductively coupled feeding method, we can obtain a wide bandwidth and a simple matching technique to directly attach to a tag chip. Also equivalent circuit model of the tag antenna is presented and unknown variables are analyzed and checked. Therefore the tag antenna can be designed for various tag chips and frequency ranges.

A Novel Compact Microstrip Bandstop Filter Based on Spiral Resonators

A novel compact microstrip bandstop filter using spiral resonators (SRs) is proposed. An array of SRs topology which is etched on the center line has stopband characteristics. And this microstrip bandstop filter can be implemented with very small size because of the sub-wavelength effect of SRs. The 3-cell SR filter is fabricated and verified by measurements. We have obtained low insertion loss in the passband and high rejection level in the stopband with steep cutoff. This novel structure is easy to fabricate and is a promising structure that is compatible with MMIC or PCB process.

RCS Reduction of Open-Ended Circular Waveguide Cavity with Corrugations Using Mode Matching and Scattering Matrix Analysis

A scattered radar signal by a jet engine inlet involves engine information of the target. The jet engine RCS due to the engine inlet is therefore signiflcant in radar target recognition. Accordingly, several accurate analyses of the jet engine RCS have been reported. Reduction of the jet engine RCS is also required for stealth technology. We suggest a new approach for jet engine RCS reduction that involves the insertion of many small corrugations into the jet engine inlet. The proposed jet engine structure is assumed to be a circular waveguide cavity with many corrugations. The structure is analyzed by combining a mode matching technique with a scattering matrix analysis. The proposed closed-form RCS solutions of the corrugated engine structure are validated with a MoM simulation using FEKO. The proposed closed-form solution has numerical e-ciency and rapid convergence. Using the characteristics of the solution, we simply apply a genetic algorithm (GA) to optimize the structure of the corrugations in terms of minimizing the RCS.

A Hybrid IPO-MoM Technique for Wave Scattering Analysis of Jet Engine

A hybrid iterative physical optics-method of moments(IPO-MoM) technique is presented for the analysis of jet engine structures which are both electrically large and complex. In this technique, the IPO method is used to analyze smooth inlet region and the MoM method is used to analyze electrically complex region inclusive of blades and hub. It is efficient and accurate by virtue of combining the respective merits of both methods. Numerical results are presented and validated through comparison with Mode-FDTD and measured results.

A Tunable Notch Resonator Based on Varactor-Loaded Complementary Split-Ring Resonators

In this paper, a tunable notch resonator based on CSRRs using varactor is proposed. This new resonator, called by the authors as varactor-loaded complementary SRRs (VLCSRRs), is a promising component thanks to its compact and tunable characteristic as VLSRRs.