Dual-Polarized Electronic Mode Stirring for Improved Backscatter Communication Link Margin in a Reverberant Cavity Animal Cage Environment.

It has previously been shown that the metal cages used for housing research animals resemble a reverberant cavity, presenting dense multi path interference for communication channels within the cage. This is due to the metal walls of such cages forming a resonant cavity having deep nulls at many locations within the cage volume. This creates significant challenges for neuroscience research where non-human primates are equipped with brain-computer interfaces (BCIs) to record neural activity. Prior work has shown that electronic mode stirring can be used to mitigate the deep nulls by selectively changing the electromagnetic boundary conditions on the cage walls. We present a novel dual-polarized 2.4 GHz electromagnetic mode stirring system consisting of integrated dual-polarized air dielectric patch antennas with CMOS RF switches enabling each polarization to be terminated in either a short or open condition and thus selectively changing the phase of reflection from the antennas. In initial testing over 72 surveyed locations within a test cage across the 2.4 GHz ISM band (2400–2483 MHz), dual-polarized mode stirring is shown to improve the worst-case two-way insertion loss between the BCI antenna and a cage-mounted antenna by 28.6 dB with dual-polarized mode stirring enabled, relative to without mode stirring. This approach is also shown to reduce the standard deviation of two-way insertion loss from 8.6 dB without mode stirring to 7.3 dB with dual-polarized mode stirring.