An ultrawide band (UWB) time domain (TD) radar has been developed for Time Reversal (TR) synthetic inverse scattering. This work describes the fabrication and test of a time domain TR “mirror” (TRM), which is the system that transmits, receives, and processes TR signals. Time reversal electromagnetics is a family of signal processing techniques that exploit the time reversal invariance of Maxwell equations, and allow focusing of waves in space and time with “super resolution”, i.e. beyond the classical resolution limit. In a typical TR experiment, first a pulsed signal is emitted and scattered by a target, which then acts as a weak emitter “source” toward the TRM. Then the TRM senses and records the weak scattered signal. Next, the recorded signals are time-reversed for their subsequent normalization and reradiation into the medium. The result is a signal that focuses in time and space where the target originally was, permitting localization and identification applications.
A 12 mW low power short range experimental verification of the above process in the microwave domain is demonstrated in this work. The developed system exhibits a 40 GHz useful bandwidth such as to be able to follow 12 ps transition duration signals without distortion. An antenna system was designed and fabricated to satisfy the above bandwidth specification. The backward propagation in the TR process is executed synthetically on account of the current state of the required technology to recreate ultra-fast signals of arbitrary shape.
Owing to its intrinsic TD nature, the finite difference time-domain (FDTD) method was applied as the numerical engine to simulate the electromagnetic fields in the TR process, facilitating the link between acquired data and its interpretation. The system designed showed capable of recreating in TD, with this extended bandwidth, the standard TR experiment as predicted by the theory. Hence, from real measurements the system was able to recreate synthetically space and time focusing. This kind of system could have application in subsurface target detection, trough-wall imaging and novel wireless communications.
Additionally, in this work a numerical study introducing a novel technique to estimate the (mean) effective permittivity of a random media applying TR techniques is presented, and for which high performance computing was required to process the data. The results showed that TR can be applied to determine effective permittivity of random media difficult to otherwise model deterministically.