  We present measurements of the 28 GHz self-interference channel for
full-duplex sectorized multi-panel millimeter wave (mmWave) systems, such as
integrated access and backhaul. We measure the isolation between the input of a
transmitting phased array panel and the output of a co-located receiving phased
array panel, each of which is electronically steered across a number of
directions in azimuth and elevation. In total, nearly 6.5 million measurements
were taken in an anechoic chamber to densely inspect the directional nature of
the coupling between 256-element phased arrays. We observe that highly
directional mmWave beams do not necessarily offer widespread high isolation
between transmitting and receiving arrays. Rather, our measurements indicate
that steering the transmitter or receiver away from the other tends to offer
higher isolation but even slight steering changes can lead to drastic
variations in isolation. These measurements can be useful references when
developing mmWave full-duplex solutions and can motivate a variety of future
topics including beam/user selection and beamforming codebook design.
