Microwave signal nulling using multiple antennas and time-reversal method

In this paper, we describe a multiple antenna microwave nulling technique that makes use of time-reversal concepts. The time-domain simulations and frequency domain experiments have shown that by using multiple antennas and time-reversal technique, we can maximize (focusing) as well as minimize (nulling) RF energy at active or passive target points in the medium. We have done experiments between 4 to 6 GHz in a laboratory environment. The degree of nulling as well as focusing depends on the multipath components in the channel and the bandwidth of the waveform. Using a 2-GHz bandwidth waveform, we have experimentally shown high-resolution microwave nulling results in a 2-D plane.