Locating Transient Directional Sources in Free Space Based on the Electromagnetic Time Reversal Technique

Traditional location methods such as time of arrival and direction of arrival have been widely used to locate transient radiation sources. However, these approaches neglect the directional radiation pattern of the sources. Locating directional sources is a complicated task because the waveform and the amplitude of radiated signals in the time domain vary for different directions. In this article, the ability of the electromagnetic time reversal (EMTR) technique to locate directional sources is investigated. As a typical directional source, the impulse radiation antenna (IRA) is used to validate the method. A radiation model is first established, and the time reversal procedure is carried out in the frequency domain. The amplitude of the signals is kept constant in the reverse phase in order to eliminate the distance attenuation. After analyzing the characteristics of directionality, we choose the energy criterion to estimate the position of the source since the time reversed signals would add up in phase only at the position of the source. It is shown that the point with the maximum energy of the synthesized signal corresponds to the position of the source. Numerical validations are presented and the relationship between the spatial resolution and the influencing factors such as the central frequency and the bandwidth of the excitation, the background noise level, the baseline length, and the number of sensors, are discussed in this article. Experimental results in an anechoic chamber with an impulse radiation antenna as the radiator and multiple horn antennas as the receivers are presented which confirm the ability of the EMTR-based method to locate directional radiation sources. Furthermore, we show that the location accuracy obtained with the energy criterion is better than that obtained with the ∞-norm criterion in the considered scenarios.