Y-junction circulators are commercially available up to 40 GHz with 16 dB isolation and full waveguide band operation (40% fractional bandwidths). Above 50 GHz the bandwidth is severely limited, making them unsuitable for many systems. For example, a Y-junction circulator tuned near 160 GHz typically has a 20 dB fractional bandwidth of less than 2%.

At Micro Harmonics we developed a new mm-wave hybrid circulator technology that has a 24% fractional bandwidth. Our initial prototypes cover the entire band from 150 GHz to 190 GHz with more than 20 dB isolation and less than 2.2 dB insertion loss. Measured test data are shown below. For comparison, we also show test data from a 162 GHz Y-junction circulator.

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 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 is currently working with NASA to develop hybrid circulators in additional 24% bands as indicated in the table below. The development effort will be completed in December 2023. The estimated release dates are indicated in the table. There is some flexibility in the target bands. If you have a specific band of interest, please contact us and we may be able to accommodate your needs.

Model Name EIA Flange Frequency (GHz) Est. Release Date
HC148 WR-15 54 – 68 July 2022
HC122 WR-12 70 – 88 November 2022
HC100 WR-10 84 – 104 March 2023
HC80 WR-8 107 – 133 July 2023
HC65 WR-6.5 118 – 150 October 2023
HC51 WR-5.1 150 – 190 Current
HC43 WR-4.3 200 – 250 December 2023
HC34 WR-3.4 Pending

The hybrid circulator technology is patent pending.


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