ULTRA-WIDE-BAND ELECTROMAGNETIC PULSE-PROPAGATION IN A HOMOGENEOUS, COLD-PLASMA

In this paper, we investigate the propagation of an ultra-wideband ele ctromagnetic pulse in a homogeneous, cold plasma which is used to repr esent a simplified model of the atmosphere. The standard procedure for the computation of the corresponding transient field involves the app lication of a fast Fourier transform (FFT) to a well-known, analytical , frequency-domain solution. However, because of the long tails in bot h the time and frequency domains, a large number of sample points are required to compute the transient response using this FFT approach. In this paper, we introduce a new asymptotic extraction technique which dramatically reduces the number of sample points required by the FFT. First, we review the recently derived closed-form expression for a dou ble-exponential pulse propagating in a homogeneous, collisionless, col d plasma. Since the high-frequency behavior does not depend on the ele ctron collision frequency, an analytical frequency-domain expression, which is similar in form to the one encountered for the collisionless, cold plasma and encompasses this high-frequency behavior, can be subt racted from the exact expression for the plasma with a nonzero collisi on frequency. The extracted term is evaluated analytically. The remain ing expression, which can be transformed to the time domain with a FFT , requires only a modest number of sample points. This dramatically im proves the numerical efficiency of the approach. We find that the extr acted analytical term provides a very good approximation for the early -time behavior of the transient pulse.