This paper presents an investigation of the electromagnetic signature and the coupling mechanism of quadcopter drones with incident electromagnetic (EM) wave and radar cross section (RCS) analysis. Coupling analysis is performed based on the dominant coupling path: when an incident EM wave with a magnitude of 50 kV/m contacts a commercial quadcopter drone, its motor power wires are identified as the dominant coupling path. Higher coupling voltages are obtained for frequencies that have large impedance values at both ends of the load on the motor power wire. This induced voltage can affect the integrated circuit chip on a printed circuit board, as well as parallel plate resonances. Furthermore, the RCS of a quadcopter drone is measured in the frequency range of 0.5-3 GHz. The internal-component vulnerability characteristics of quadcopters can spike at specific frequencies with high RCS values and can be analyzed with or without motor power wires. We verified these hypotheses via 2D inverse synthetic aperture radar images, and we analyzed the results by comparing the empirical and full-wave simulation values.INDEX TERMS Coupling analysis, input impedance, inverse synthetic aperture radar, parallel plate resonance, quadcopter drone, radar cross section, vulnerable path, wire coupling.

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In this paper, to analyze the dispersive characteristics of plasma, a dispersive model suitable for the finite-difference time-domain (FDTD) method is proposed. The dispersive characteristics of plasma with varying electrical properties according to frequency were accurately and efficiently expressed using the modified Lorentz dispersive model. The coefficient of the modified Lorentz dispersive model was extracted by applying complex curve fitting based on the weighted least squares method. The method of applying the modified Lorentz dispersion model to the FDTD is discussed. The plasma model based on the modified Lorentz dispersion model proposed in this paper was verified to match the data of the dielectric barrier discharge (DBD) plasma generator from dielectric slab equivalent modeling. The accuracy of the proposed FDTD algorithm based on the modified Lorentz dispersive model was verified by comparison with the results of the broadband radar cross-section (RCS) measurement experiment.

A dielectric barrier discharge (DBD) plasma generator with a face-to-face multilayer structure for radar cross section (RCS) reduction is designed. The generator includes two electrodes of 16×0.5 cm 2 size, facing each other. Because the electrodes are on the plane that is parallel to the direction of the incident wave, the effect of the generator on the RCS of the target is significantly reduced, particularly when compared to conventional parallel plate-type generators. This simplifies the design procedure for the DBD generator and maximizes the effect of the plasma on RCS reduction. For experimental verification, 42 layers of the proposed generator with a distance of 5 mm between the two electrodes are stacked to reduce the RCS of a 20×20 cm 2 -sized copper plate. Experimental results demonstrated a reduction of approximately 3.2 dB in the RCS in the X-band.

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