In order to realize superconductive microwave devices with large tuning characteristics, we have studied a mechanically tunable superconductive resonator beneath a dielectric and/or magnetic floating plate (FP) as a first step. The resonator consists of a half-wavelength coplanar waveguide (CPW). The principle of the mechanically tunable method is that variations of the effective permittivity and/or the effective permeability for the microwave waveguide line can be obtained by changing the distance between the resonator and the FP. In computer simulations of electromagnetic fields for the mechanically tunable half-wavelength CPW resonator, we have obtained a large shift of the resonant frequency with a band of 1.75 GHz to 7 GHz (tunability is approximately 25%) using the (La0.3Sr0.7)(Al0.65Ta0.35)O3 (LSAT) single crystal (dielectric constant (εr) = 22.8, loss tangent (tanδ) = 1.7 × 10−4) as the FP. Based on the results, we have performed an experiment using a half-wavelength CPW resonator made from YBa2Cu3O7−δ thin film and the LSAT FP. The result shows a drastic resonant frequency shift of approximately 1.36 GHz (tunability is approximately 20%) when the LSAT FP is moved, using an electromagnetic actuator. In this experiment, it is also noted that the insertion loss is quite low, less than 0.8 dB, compared to previous reports for various tunable filters. Moreover, we have also measured the tuning characteristics with a TiO2 single crystal (εr = 85.4, tanδ = 2.5 × 10−4) as the FP. As a result, we have obtained quite large tuning characteristics of approximately 2 GHz (tunability is approximately 28%).
Pr1−xCaxMnO3 (PCMO) (x = 0.15∼0.30) has good dielectric and magnetic properties at the microwave band. High-Tc superconductor (HTS)/ferromagnetic PCMO heterostructure has a high potential for superconducting tunable microwave filters and superconducting magnetostatic wave (MSW) devices. In order to demonstrate the preparation possibility of superconducting MSW devices, we investigated the microwave behaviour of YBa2Cu3O7−δ(YBCO)/PCMO heterostructures fabricated by a pulsed laser deposition technique on (La0.3Sr0.7)(Al0.65Ta0.35)O3 (100) substrate. We also fabricated superconducting MSW-band elimination filter (BEF) with YBCO/PCMO structure. The MSW-BEF exhibited notch characteristic that is caused by the energy conversion due to the coupling between the MSW mode and the transverse electromagnetic mode. These results suggest that the HTS/PCMO heterostructure is effective for the superconducting MSW application.
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