Micro Harmonics markets two types of broadband mm-wave hybrid circulators. One type has a 24% fractional bandwidth and is available in every standard waveguide band from WR-15 through WR-3.4 as indicated in the table below. The second type is designed to cover full rectangular waveguide bands having fractional bandwidths in excess of 40%. The first prototype of the full band model was recently tested in the WR-6.5 band. Additional full band models are planned for development in every band from WR-15 to WR-3.4.
Historically, the Y-junction has been the most common type of circulator at mm-wave frequencies. A Y‑junction comprises a ferrite core located at the convergence of three waveguides. At the higher mm‑wave frequencies, the Y-junction has a narrow bandwidth and is difficult to tune. The theory of operation and architecture of the hybrid circulator are very different from the Y-junction. The hybrid circulator comprises a Faraday rotator and an orthomode transducer (OMT). Since both the Faraday rotator and OMT are inherently broadband, the hybrid circulator is also broadband. A comprehensive technical description is given by D. W. Porterfield, “Broadband Millimeter-Wave Hybrid Circulators,” IEEE Trans. Microw. Theory Techn., vol. 71, no. 8, pp. 3501-3507, Aug. 2023. The hybrid circulator technology is patent pending.
The bar chart below shows fractional bandwidths for the hybrid circulators and Y-junction circulators. The bandwidth of the Y-junction circulator steadily drops as the frequency increases, approaching only 2% at 160 GHz. We define the 20 dB bandwidth as the band over which the isolation between circulator ports is more than 20 dB.
Sample test data from one of our WR-5.1 hybrid circulators are shown in the lower graph along with test data from a Y-junction circulator for comparison. This hybrid model is designed for 24% bandwidth. The insertion loss of our WR-5.1 hybrid circulator is less than 2.2 dB.
Measured data for the full band WR-6.5 hybrid circulator are shown in the graph below. Isolation is greater than 20 dB. Return loss is greater than 15 dB. Insertion loss is less than 1.5 dB across most of the band. This level of performance has never been achieved before in a D band circulator.
At Micro Harmonics, the Y-junction circulator is being replaced by the broad band hybrid circulator. But for narrow bandwidth applications, we continue to offer a line of Y-junction circulators covering sub-bands within the WR-15, WR-12, WR-10, and WR-8 bands (50-140 GHz). These circulators exhibit state-of-the-art performance in terms of high isolation, low-insertion loss, and low port reflections. Special order designs optimized for specific sub-bands are considered on a case-by-case basis.