The transient process of propagation pattern in rectangle waveguide is analyzed theoretically and the analytical formulas of electromagnetic wave transient response excited by impulse
step signal and Gaussian pulses wave in the wave-guide are given. The time-frequency analysis method is used to analyze the transient response characteristics of signals propagated along waveguide and open cavities scattering signal. Through analyzing it is found that the scattering signal contains resonance pattern that is related with the size and shape of cavities when an electromagnetic pulse signal is projected on open cavities. With different open cavity target the resonant frequency will be different in scattering subsequent signal. The targets with open cavities can be identified by extracting the resonance feature in scattering signal.
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