A Q-Band Gyroelectric Waveguide Isolator

This paper presents a waveguide isolator working in the Q-band by utilising the gyroelectric effects of magnetised semiconductors. After developing an exact mathematical approach for analysing a rectangular waveguide loaded with layered media, the complex propagation constants for a WR-22 waveguide loaded with an Indium Antimonide (InSb) slab at 77 K are calculated. It is found that the structure exhibits strong nonreciprocity for a range of frequencies when the InSb is biased with a specific D.C. magnetic flux. This behaviour is then utilised to design an isolator working at 48 GHz by magnetically biasing the InSb with a D.C. magnetic flux of 0.6 T. Next, the performance of this isolator is verified via simulation and measurements, and both resulted in more than 21 dB isolation at the frequency of operation. Unlike classical ferrite nonreciprocal devices, the operation of the gyroelectric devices can be extended up to the THz frequency ranges. This potential is demonstrated here by proposing another isolator to work at 143 GHz by loading a 4 mm long WR-06 waveguide with InSb slab at 77 K, and biasing it with a magnetic flux of 0.15 T. Simulation results show more than 30 dB isolation at the frequency of operation, which prove the advantages of utilising the gyroelectric effects in designing compact millimetre and sub-millimetre wave waveguide isolators.