Broadband Millimeter-Wave Hybrid Circulators for NASA Missions

Y-junction circulators are used to direct signal flow in millimeter-wave (MMW) transmit/receive systems including radar and high speed data links. At the heart of the device is a ferrite core located at the junction of three waveguides. The magnetically biased ferrite is non-reciprocal which gives rise to the unique circulator behavior. Circulators are available with full waveguide band operation up to 40 GHz, although the isolation is generally less than 16 dB. At higher frequencies the bandwidth is severely limited by the ferrite material properties. Y-junction circulators operating between 50-90 GHz typically have bandwidths near 2nbsp;GHz and above 100 GHz the bandwidth is only 1 GHz, making them unsuitable for many systems.What is needed is an all-new approach to the problem. We propose a novel hybrid circulator comprising an orthomode transducer (OMT) and a modified Faraday rotation isolator. These two devices can be combined to form a hybrid circulator that can operate with very high isolation over nearly full rectangular waveguide bands. Circulators with this level of performance simply do not exist in the commercial market. The hybrid circulator is thus an enabling technology, offering significantly improved performance over the current state-of-the-art. At the end of the Phase I contract, we will deliver a prototype hybrid circulator covering the 150-190 GHz band to NASA. This component will find application in NASA G-band radar systems designed for future cloud, water, and precipitation missions.Micro Harmonics is uniquely qualified to carry out this research. We have demonstrated the accuracy of our ferrite models through previous highly successful NASA SBIR contracts. We currently produce the most advanced Faraday rotation isolators on the global market with insertion loss less than 2 dB in the WR-3.4 band 220-330 GHz. We are extending coverage to 500 GHz. With the proposed SBIR funding we have an opportunity to transform the MMW circulator technology.