Proceedings PaperFrequency Modulated (FM) And Amplitude Modulated (AM) In Millimeter Radar Due To Vibrating Structures
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A theoretical analysis of the spectral content of a frequency modulated (FM) and amplitude modulated (AM) electromagnetic plane wave is presented. An unmodulated transmitted millimeter wave is modulated when reflected from a sinusoidally oscillating structure. The FM results from the doppler effect, while AM results from the optical properties (antenna beamwidths, radar cross sections (RCS)) of millimeter waves. The purpose of the analysis is to investigate the effect of the AM on the spectral lines resulting from FM. It is anticipated that AM is largely due to the RCS characteristics of the vibrating structure. For FM only, the amplitude of the first side band (spectral line) is maximized when the transmitted wavelength is approximately seven times the structure oscillation displacement amplitude. When the waveform also has AM, the spectral line amplitudes are increased, and the maximization criterion no longer applies.