The results of experimental research and development of the diffraction radiation oscillator with a periodic structure in form of a reflective double comb and with frequency tuning on mutual coupled modes in its open resonant system were presented. As an operating mode we chose the mutual coupled modes TEM002 → TEM101, which arise in the open resonant system with the shift between mirrors symmetry planes. To analyse its features, a rigorous electrodynamical 2-D model of the open resonant system was used, and the optimal shift width was established. As a result, the operation on the mutual coupled modes allowed to extend the frequency tuning range without failures in output power and to exclude the influence of higher-order modes (TEM20q, TEM30q etc.) on the output characteristics of the oscillator. The research has been carried out in Ka band.
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