Planar HTS structures for high-power applications in communication systems

The use of rotational symmetric modes of superconductive disk (ring) resonators in order to increase the power handling capability of planar filters has been proposed. Several YBCO disk resonators on LaAlO₃ and sapphire substrates have been measured as one- and two ports. The unloaded Q-factor of the resonators has been measured to be greater than 10⁵ up to the oscillating power of 50 kW. Experimental results obtained show that a disk resonator can be used as a building block for low insertion loss, sharp skirt high-power planar filters at low GHz frequency range and temperatures of around 60 K.     

Thin Film Tl-Based HTS Microwave Devices

Linear microstrip resonators suffer from high peak current density inside the resonators which limit the power handling characteristics. To realise higher power filters for cellular applications it is possible to use two dimensional microstrip resonators (such as disks) to equalise the internal current distribution. We have designed and tested such microstrip resonators, fabricated from TBCCO 2212 thin films deposited by RF sputtering onto 10×10mm and 20×20mm LaAlO₃, substrates. The R_s of such films has been measured at 24 GHz using a sapphire dielectric resonator and shown to be less than 500 scaled to 10 GHz and at 80K. Q values of 3-12 GHz disk resonators have demonstrated considerable improvements when compared to both linear HTS microstrip resonators and comparable copper disk resonators. Additionally, the power handling of such resonators has been shown to be superior to that of conventional linear resonators fabricated from similar material.     

Conditions for and limitations of high-power handling capabilities of planar YBa2Cu3O7-x filters

The conditions for the design of compact high-power HTS filters are deduced from basic considerations, and related to the microwave properties of the HTS films and the substrates. Potential mechanisms limiting the linear microwave response of HTS films are analyzed systematically. Magnetic and thermal field breakdowns are found to confine the power handling capability to comparable field levels. While magnetic limitation is related to flux penetration at the lower critical field B_c1, thermally induced quenches occur dependent on the presence of defects and on the thermal conductivity of the substrate. The detrimental role of film inhomogeneities for the linear microwave response is confirmed experimentally for microwave fields at 19 GHz and for dc fields at 87 GHz.     

A Novel HTS Shuttle-Shape Resonator for High-Power Application

A novel shuttle-shape microstrip resonator for high-power high-temperature superconductor (HTS) filters is presented. By transmission line theory analysis, it can improve the power handling capability up to 20%, depending on the configuration of the resonator. To confirm this analysis result, two 2-pole HTS filters based on shuttle-shape resonator and rectangle resonator were simulated. Considering the limitation of computer memory, a moderate configuration was chosen for HTS filter design. By computer simulation, a comparison between filters with shuttle-shape and rectangle resonators showed a 10% increase in power handling capability. The HTS shuttle-shape filter was fabricated and tested. It has a center frequency of 2022 MHz with a 2.5% bandwidth. The measured power level was over 34 dBm at 70 K with sufficiently low insertion loss.     

High-temperature superconducting dual-mode resonator on (100) MgO substrate

We report, for the first time to our knowledge, a clear resonant peak split in the range of 7.7–9.7 GHz in a perturbed dual-mode disk-type resonator (DMDR) made of YBa₂Cu₃O_7–x (YBCO) superconducting thin film on MgO substrate. Epitaxial YBCO superconducting thin films were grown on (100) MgO substrates by pulsed laser deposition technique. The critical temperature of superconducting thin film on MgO substrate was 85 K. Superconducting dualmode disk resonators were designed by microwave design software, EEsof, and patterned by photolithography and a wet-etch process. The unloaded quality factor (Q_UL) of the superconducting DMDR was found to be 1,312 at 77 K. We believe this type of DMDR can be utilized for dual-mode resonator-based filters for satellite communications.     

Nonlinear Power Handling of YBa2Cu3O7−x Films and Microwave Devices

Physical mechanisms which limit the power handling of YBa₂Cu₃O_7?x films and devices are discussed in terms of a quantitative classification scheme. The possible limitations are devided into magnetic or thermal, and global or local in nature. Analytical estimations are compared with measurements of YBa₂Cu₃O_7?x films (Ø = 1″–2″) using a niobium-shielded sapphire resonator at 19 GHz, and disk resonators at 2 GHz. Magnetic effects are found to play an essential role in nonoptimized films in terms of weak-links, and in high-quality films if the lower critical field Bcl is reached. The majority of films and disk resonators appear to suffer from microwave heating. Global heating appears predominantly at CW operation. Local heating results mainly from defects in films of medium quality. Defect-induced quenches are observed at moderate field levels, sometimes resulting in an irreversible degradation of the power handling.     

Dual-mode microstrip filters with adjustable transmission zeros

A new type of dual-mode microstrip square-loop resonator that produces asymmetrical frequency responses is proposed. The coupling between degenerate modes of the proposed dual-mode resonator is discussed depending on the perturbation size. The effect of non-orthogonal input/output feed lines located along a straight line on the frequency response is investigated using full-wave electromagnetic simulations. Two second-order bandpass filters using this type of dual-mode microstrip resonator are designed, fabricated and measured to demonstrate the dual-mode microstrip filters exhibiting transmission zero (TZ) shifting property. The one of the second-order filters produces a filter characteristic with two TZs in the upper stopband, whereas the other one has two TZs in the lower and upper stopbands. The shifting property of one of the TZs from one side of the passband to the other side is realised by only changing the perturbation size. The fourth-order filters of this type are also investigated. Both simulated and measured results are presented.     

Compact double-mode cross-coupled microstrip bandpass filter with tunable transmission zeros

A compact double-mode cross-coupled microstrip bandpass filter with an asymmetric frequency characteristic and three transmission zeros is presented. The bandpass filter consists of a cross-coupled gap and a double-mode resonator of a half-wavelength line with a shunt-stepped-impedance open stub. In comparison to the conventional square loop dual-mode resonator, the proposed double-mode resonator achieves a 59% size reduction. The parametric studies on the electrical length of the open stub and the capacitance of the cross-coupling are provided in order to gain a better insight into the transmission poles and zeros. Then, a bandpass filter is designed, fabricated and tested to validate the design concept. From 2.3 to 2.5 GHz, the return loss is better than 10 dB and the insertion loss is <1.5 dB. There are three transmission zeros in the upper stopband at 2.8, 3.4 and 4.9 GHz.     

Nonlinear Power Handling of YBa2Cu3O7?x Films and Microwave Devices

Physical mechanisms which limit the power handling of YBa₂Cu₃O_7–x films and devices are discussed in terms of a quantitative classification scheme. The possible limitations are devided into magnetic or thermal, and global or local in nature. Analytical estimations are compared with measurements of YBa₂Cu₃O_7–x films (Ø = 1–2) using a niobium-shielded sapphire resonator at 19 GHz, and disk resonators at 2 GHz. Magnetic effects are found to play an essential role in nonoptimized films in terms of weak-links, and in high-quality films if the lower critical field Bcl is reached. The majority of films and disk resonators appear to suffer from microwave heating. Global heating appears predominantly at CW operation. Local heating results mainly from defects in films of medium quality. Defect-induced quenches are observed at moderate field levels, sometimes resulting in an irreversible degradation of the power handling.     

On the Power Handling Properties of High Temperature Superconducting Microwave Contiguous Duplexer

The power handling properties of a high temperature superconducting (HTS) microwave contiguous duplexer are measured in this letter. The HTS contiguous duplexer was fabricated using YBa₂Cu₃O₇ (YBCO) thin films on a 0.5-mm-thick LaA1O₃ substrate, operation frequencies of which are centered at 3.25 GHz and 3.75 GHz with 500-MHz-wide channels. The tested frequency response of power handling property of the HTS contiguous duplexer shows that there is a decreased power handling property on the crossover region; however, this microwave nonlinearity does not affect the engineering application of HTS contiguous duplexers and multiplexers.