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Novel planar construction of high-temperature superconducting filters that improve power-handling capability is proposed. Split open-ring resonators are developed to be used in reaction-type transmitting filters that have very sharp bandstop characteristics. Resonator structures to achieve high-unloaded Q-factors and low radiation as well as low surface current densities in the passband are numerically investigated for 5 GHz band operation. Low surface current densities reduce the generation of intermodulation distortions. Measurements confirm an unloaded Q-factor of 68 000 and third intermodulation-distortion of -82 dBc at 30 dBm input power.Introduction: Planar microwave filters based on high-temperature superconducting (HTS) thin-films achieve simultaneous steep skirt characteristics, low insertion loss, and small volume at the same time, unlike conventional room-temperature devices [1].However, HTS microwave filters for high-power applications that have the same performance as HTS receiving filters have not been realised so far. This is mainly due to surface-current concentrations on the devices and the generation of intermodulation distortion [2,3]. We proposed the HTS reaction-type transmitting filter (HTS-RTF) to suppress adjacent noise generated by the power amplifier [4]. Since reaction-type resonators do not resonate with high-power fundamental signals, an HTS-RTF offers both high-power handling capability and sharp cutoff characteristics.For practical applications in the microwave region, however, the resonators must achieve low surface current densities in the passband and high-unloaded Q-factors as well as low radiation levels.This Letter proposes a novel HTS split open-ring resonator (SORR) with improved power-handling capability for HTS-RTFs. First, novel SORR structures that reduce maximum current densities while offering both high-unloaded Q-factors and low radiations are investigated in the 5 GHz band. Secondly, to further improve the current density dispersion effect, additional slits are added to the resonator surface. of exceeding HTS critical current density or generate intermodulation distortion. To reduce these induced current densities, a 2 GHz SORR was proposed and the edge-current dispersion effect was numerically investigated in a previous letter [4].Additional investigations are carried out to improve resonator characteristics in the 5 GHz band. The investigation is based upon full wave electromagnetic analysis using the method of moments. The geometry of a 5 GHz SORR is shown in Fig. 1a. The material of the substrate is assumed to be MgO with dielectric constant of 9.7, a loss tangent of 5.5 × 10 -6 , and a thickness of 0.5 mm. The HTS thin-film material is assumed to be YBCO with conductivity of 6.5 × 10 12 S/m and thickness of 0.5 um. In addition, a shielded box with finite conductivity the top plate height of which is 5 mm is taken into account. Q-factor of the SORR is 47 800 at g = 0.4 mm. For both resonators, diameters and distance of resonators to feedlines are adjusted to ach...

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Abstract.A new kind of high-temperature superconducting (HTS) transmitting filter based on a reaction-type resonator is presented. The purpose of an HTS reaction-type filter (HTS-RTF) is to eliminate the intermodulation distortion noise generated by microwave power amplifiers such as those employed in mobile base stations. An HTS-RTF enables both higher power handling capability and sharper cutoff characteristics compared to existing planar-type HTS transmitting filters, since a reaction-type resonator does not resonate with high-power fundamental signals. To achieve steep skirt characteristics and high-power handling capability simultaneously, a 5-GHz three-pole HTS-RTF using split open-ring resonator is designed. This split open-ring resonator offers low maximum current densities and a high-unloaded Qfactor with low radiation. The designed prototype filter has Chebyshev characteristics with a centre frequency of 4.95 GHz and a bandwidth of 1.5 MHz. The HTS-RTF is fabricated using a double-sided YBa 2 C 3 O 7−δ thin film deposited on a 0.5 mm thick MgO substrate. The measured filter shows an insertion loss of less than 0.1 dB and a third intermodulation distortion value of -56.7 dBc for a 40 dBm passband signal. In addition, adjacent channel leakage power ratio (ACLR) measurements using an actual Wideband CDMA signal confirm an ACLR improvement of about 10 dB for a four-carrier signal with power of up to 40 dBm.