A Frequency Domain Approach For Time-reversal Of Microwave Impulses
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In this thesis, a compact and low-cost electronic circuit system is designed for time-reversal of microwave impulses with nanosecond and sub-nanosecond temporal durations. A frequency domain approach is adopted in order to avoid high sampling rate in time. The proposed system obtains the discrete spectra of input impulses first, then realizes time-reversal in frequency domain, and finally synthesizes the time-reversed impulses using discrete continuous wave elements. It is composed of commercially available circuits including oscillators, mixers/multipliers, band-pass-filters, amplifiers, and switches, hence embodies low-cost system-on-chip implementation. The proposed time-reversal circuit's performance is verified by Advanced Design System (ADS) simulations, with most non-idealities of realistic circuit components taken into account. Simulation results show that, microwave impulses with about 1 ns temporal width and 3 - 10 GHz spectral coverage are reliably reversed in time, even with presence of strong noise. Furthermore, the proposed time-reversal circuit system is validated in the context of electromagnetic propagation in complex environments. Specifically, circuit-electromagnetic co-simulation is carried out to investigate the "focusing" phenomena of time-reversal. A full-wave Maxwell's equations solver based on Finite Difference Time Domain (FDTD) method is developed to model electromagnetic propagation, and it is coupled to ADS circuit simulator. The FDTD solver is implemented on parallel cluster Message Passing Interface (MPI), in order to relieve high computational complexity due to complex environments. Two real-world problems (one is for wireless communication and the other is for radar detection) are investigated. Desired "focusing" phenomena in both space and time are demonstrated by the simulation results, which conclude that the proposed time-reversal system can be deployed in practical time-reversal communication and radar applications.