A Millimeter-Wave Gyroelectric Waveguide Isolator

In this paper, a new type of millimeter-wave waveguide isolator is demonstrated. After developing an analytical model for a rectangular waveguide loaded with stratified media, all the modes propagating through the structure are found. Isolators are then designed by utilizing the frequency ranges where high nonreciprocal attenuation is identified. Here, an isolator is designed to work within the Ka-band by loading a WR-28 waveguide with a transversely magnetized indium antimonide (InSb) slab cooled to 77 K. Measured performance shows more than 20-dB isolation with 1-dB insertion loss, which agrees with theoretical predictions. Moreover, the effects of changing the magnetic bias (B
₀
) and adding dielectric layers above the InSb slab were analyzed theoretically and verified through measurement. Results prove the possibility of achieving high isolation using a weaker magnetic bias by topping the gyroelectric slab with dielectric layers. Nonreciprocal behavior was also demonstrated using an isolator working at 105 GHz, where simulated results show more than 33-dB isolation with 1.16-dB insertion loss. The results presented in this paper could pave the way toward the realization of nonreciprocal components working in the submillimeter-wave and terahertz frequency ranges, where the performance of the classical ferrite device deteriorates.