Generalized Theory of Concurrent Multimode Reciprocal and/or Nonreciprocal SIW Ferrite Devices

In this work, we propose, develop, and demonstrate a fundamental and comprehensive theoretical foundation for the first time to formulate and devise known and unknown reciprocal and/or nonreciprocal ferrite components with arbitrarily concurrent multimode features based on the substrate-integrated waveguide (SIW) technology. To achieve such a universal design, a nonreciprocal unit cell (NRUC) is first defined and characterized. Then, an approach is proposed and investigated to deploy a sufficient number of NRUCs next to each other as a kernel multimode SIW topology. The kernel configuration transforms the incident guided-wave into several separate segments, propagating in parallels independently and along each NRUC, which can be manipulated separately. This methodology grants a general solution to forge ferrite components in a multimode configuration, discussed in detail to corroborate the proposed generalized theory. Finally, two multimode components are studied and demonstrated for the first time as application examples for the proposed theory. Namely, a dual-mode circulator and a triple-mode gyrator are prototyped, fabricated, and measured, exhibiting an excellent agreement with simulation results that effectively validate the presented theoretical foundation in this work.