Microwave · INOGYRO joint lab · March 16, 2022
A new design method for dual-band circulators operating under weak bias fields
Ferrite circulators are non-reciprocal devices essential to wireless communication systems that use the same antenna to transmit and receive simultaneously. They route signals according to where they come from, favoring the propagation of the electromagnetic wave in one direction rather than the other.
The proliferation of wireless applications often calls for several frequency channels: designing multiband microwave devices is therefore becoming a major asset for data transmission systems.
INOVEOS and XLIM have been working for several years on original multiband circulator designs to meet these new needs.
A first proof of concept of a dual-band ferrite circulator [1], operating in two bands simultaneously, was demonstrated in 2017. Its circulation bands were still narrow and the spacing between them could not be chosen. Two new prototypes [2] have since widened these bands by exploiting the weak-field operating region. They also showed that the geometry of the center conductor determines the spacing between the two bands, which leads to complex geometries that had never been modeled analytically.
A new analytical method was therefore developed to match ferrite resonators with complex center conductors over two bands at once. It consists of computing the resonator’s impedance matrix in order to determine the matching network that optimizes the circulation function. The method was validated by measuring a single-band circulator with a triangular center conductor and a dual-band circulator with a stub-loaded Y conductor. Finally, this work was carried over to microstrip technology, to reduce size thanks to the substrates’ permittivity.
[1] H. Turki, L. Huitema, T. Monédière, B. Lenoir and C. Breuil, “New Concept Validation of Low-Loss Dual-Band Stripline Circulator,” IEEE Transactions on Microwave Theory and Techniques, vol. 67, no. 3, pp. 845–850, March 2019, doi: 10.1109/TMTT.2018.2890632.
[2] V. Olivier et al., “Dual-Band Ferrite Circulators Operating on Weak Field Conditions: Design Methodology and Bandwidths’ Improvement,” IEEE Transactions on Microwave Theory and Techniques, vol. 68, no. 7, pp. 2521–2530, July 2020, doi: 10.1109/TMTT.2020.2988003.
