We numerically and experimentally investigate the effective permittivity of 2D fiber composite materials with arbitrary fiber orientation at microwave frequency. We focus on the effect of fiber orientation distribution (FOD) rather than on the effect of fiber content, aspect ratio, and the matrix itself.We use the generalized equivalent conductor (GEC) method to study the electromagnetic behavior of fibers with an arbitrary orientation distribution numerically. For experimental verification, we measured the transmission coefficient of three cases of models using the free space measurement. The measurement models are classified into three categories according to the FOD. Good agreement is found between the measured and calculated effective permittivities. We also calculate the dielectric dispersion with respect to the standard deviation and frequency, and construct a dispersion curve using curve-fitting from the Lorentz model. The Lorentz model with fitting parameters shows that the FOD does not affect the resonance frequency and quality (Q) factor but only the resonance peak.
This paper proposes a two-dimensional (2-D) inverse synthetic aperture radar (ISAR) imaging method with nonuniformly obtained angle samples. A one-dimensional (1-D) radar image, a range profile, is obtained using frequency samples within a given bandwidth. 2-D ISAR images are then obtained by acquiring the Doppler spectrum using range profiles obtained from multiple observation angles having a constant interval. However, when ISAR images are obtained by applying the range-Doppler imaging method for a target scattered signal with nonuniform angle samples, a clear image cannot be obtained. In this paper, we propose a method to generate a covariance matrix from a nonuniform angle sample and obtain an ISAR image based on the multiple signal characterization (MUSIC) technique. The proposed method can be applied to the target scattering signal using a search radar, which observes target with nonuniform aspect angles. We present a scattering signal model of a target for the search radar and provide ISAR images obtained by applying the proposed method to simulated and measured data, respectively. Results reveal that the proposed method improves image quality and reduces computation time compared to the conventional method.
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