Hybrid Circulators

Micro Harmonics has developed a new mm-wave hybrid circulator technology that has a 20 dB fractional bandwidth* of 24% in every waveguide band from WR-15 through WR-3.4. In contrast, the bandwidth of a Y-junction circulator degrades rapidly at the higher mm-wave bands. Test data from our WR-5.1 hybrid circulator are shown in the lower graph along with test data from a Y-junction circulator for comparison. The insertion loss (not shown) of our WR-5.1 hybrid circulator is less than 2.2 dB.

*20 dB bandwidth – The band over which the isolation between circulator ports is more than 20 dB.

The theory of operation for the hybrid circulator is very different than the Y-junction. In the hybrid, the circulator function is achieved in a unique way that circumvents the bandwidth limitations found in the Y-junction. Hybrid circulator development is currently limited to frequencies below 400 GHz due to practical limitations imposed by the fabrication process. A photograph and dimensional sketch of a WR-5.1 hybrid circulator prototype are shown below. A more comprehensive technical description is given in the following paper: D. W. Porterfield, “Broadband Millimeter-Wave Hybrid Circulators,” in IEEE Trans.  Microw. Theory Tech., doi: 10.1109/TMTT.2023.3239886.

A WR-5.1 circulator with a 24% fractional bandwidth is a remarkable result. In fact, this would have to be considered an enabling technology. But the good news gets even better. In theory, the hybrid circulator can be designed to cover full rectangular waveguide bands with fractional bandwidths exceeding 40%. This requires a change in the geometry that is both more complicated and more costly to machine. Therefore, the immediate development efforts will continue to be in 24% fractional bands.

Micro Harmonics has worked with NASA to develop a line of hybrid circulators in additional 24% bands as indicated in the table below.