HXI developed a series of products in WR-12 specifically designed for the testing of integrated circuits and modules in the unlicensed bands.
Among the products are HXI's waveguide isolators, HMI12-387-67.5-7.0.
This product covers the complete band from 64.0 to 71.0 GHz without the high loss and long insertion length of a faraday-type isolator.
HMI12-387-67.5-7.0 datasheet