Reflective Power Limiter for X-Band With HTSC Switching Element

This paper presents a new type of power limiter (PL), using superconducting-to-normal state phase transition in high-temperature superconductor. The presented device differs from the existing ones mainly in the reflective principle of its operation. In fact, the PL is a three-resonator microstrip filter, whose resonators are configured and arranged in such a manner that coupling coefficient between the outer resonators is equal to zero and the inner one has a gap in the middle section shunted by a high-temperature superconducting (HTS) film element. In small-signal mode, the HTS element is in low-loss state, and the device is essentially a three-pole filter with low transmission loss. When the level of the signal exceeds the threshold, the HTS element transits to the high-loss state, and the Q-factor of the inner resonator falls, breaking the coupling in the structure. This leads to the corresponding increase in the PL's transmission loss due to reflection. The higher the level of incoming power, the more the Q-factor falls. The PL operating frequency is 8 GHz with 8.5% fractional bandwidth. It remains operable up to 40 W of input power, providing 38-dB limitation.