N. Sekiya

Design and Performance of Transmit Filters Using HTS Bulk Resonators for IMT-Advanced Applications

A transmit band pass filter using circular-disk high-temperature superconductor (HTS) bulk resonators was designed with a 5.0 GHz center frequency and a 100 MHz bandwidth for use in international mobile telecommunication (IMT) advanced applications. The frequency response and electromagnetic field were calculated using a three-dimensional simulator. The mode of the resonator was used because it had the smallest diameter. Using stripline (SL) resonators enhanced both the unloaded quality factor and the coupling between the input/output ports and resonators. The frequency response of the designed SL 3-pole Chebyshev filter meets the requirements of IMT-Advanced applications. Additionally, the maximum surface current of the HTS bulk filter was approximately 86% less than that of a conventional hairpin filter.

Improvement of Filter Properties Using Sapphire and Nickel Rod Trimmers

We have examined the improvement of filter properties using sapphire and nickel rod trimmers. We measured the resonance frequency of the hairpin resonator in the filter, and examined the difference between the simulated and measured values. When the measured resonance frequency was lower than the simulated frequency, we used a nickel trimmer to increase the resonance frequency, and when high, a sapphire trimmer to decrease the frequency. Our results showed that the use of sapphire and nickel rod trimmers is effective in improving the frequency response of HTS bandpass filters.

Design of Miniaturized HTS Dual-Band Bandpass Filters Using Stub-Loaded Meander Line Resonators and Their Applications to Tri-Band Bandpass Filters

We have designed a miniaturized high-temperature superconducting dual-band bandpass filters (DBPFs) using stub-loaded meander line resonators and their applications to tri-band bandpass filters (TBPFs). The DBPF enables independent control of the center frequencies of the first and second bands. The bandwidths of the DBPF can be flexibly adjusted using a capacitance-loaded microstrip line between the resonators. The DBPF was designed and analyzed using an electromagnetic simulator and fabricated using an YBa2Cu3Oy thin film on an Al2O3 substrate. The center frequencies are 3.5 and 5.0 GHz; two bands have 2% bandwidth. The measured frequency responses of the DBPF were in good agreement with the simulated frequency responses. The TBPF was realized by combining the DBPF and a single-band bandpass filter (SBPF) that uses a folded stepped-impedance resonator with common input and output. The DBPF constructs the first and third bands of 3.5 and 5.0 GHz, and the SBPF forms the second band of 4.25 GHz. The frequency responses of the simulated TBPF meet the design parameters.

Comparison of power handling capabilities of sliced and conventional microstrip line filters

We examined a high power filter using a sliced microstrip line. We simulated the current distribution in the microstrip line by using electromagnetic field analysis software. The current flowing along the outer edge of the sliced microstrip line was less concentrated than in the conventional microstrip line. The electric test power of the sliced microstrip line filter was larger than that of the conventional filter. The electric proof power of the filter can be estimated from the current flowing along the outer edge of the microstrip line.

Novel HTS Double-Strip Resonator for High Power Application

The use of a double-strip resonator is proposed for improving the power handling capability of high-temperature superconductor transmit filter with stripline structure. A double-strip resonator reduces the current concentration at the edges of the resonator compared with that of a conventional single strip resonator due to the increase of the effective film thickness. A double-strip 2-pole filter with a 5.0-GHz center frequency and 100-MHz bandwidth and with an Al2O3 substrate was designed and fabricated. An electromagnetic simulator based on the moment method was used to design and investigate the filter. To suppress spurious resonance of odd mode near the pass band, we investigated the input/output structure. The maximum current densities at the edges of the resonator as a function of frequency were simulated. The results showed that the maximum current density in the filter was approximately 30% less than that of the conventional single-strip filter. The measured frequency response of the filter was in reasonable agreement with the simulated one.

Design and Fabrication of 5 GHz Miniaturized Bandpass Filter Using Superconducting Microstrip Quasi-Spiral Resonators

We propose a miniaturized novel microstrip quasi-spiral resonator (QSR) system composed of rewound-type spiral resonator and c-type spiral resonator. We have also designed a 5 GHz superconducting 4-pole bandpass filter (BPF) using QSR for international mobile telecommunication (IMT)-advanced base station receiver applications. The filter has been fabricated using a single-sided MgB2 superconducting thin film deposited by thermal co-evaporation technique. The measured performance of the BPF has been found to show close agreement with the simulated one.

Design of HTS Modified Double-Strip Resonator Filter Structure for Transmit Filter Applications

A high-temperature superconductor modified double-strip resonator filter structure for transmit filter application is presented. The filter is constructed with a double-strip resonator and a center pin of the SMA connector as a feed line for improving the power handing capability and frequency responses. A double-strip resonator reduces the current concentration at the edges of the resonator compared with that of a conventional single strip resonator due to the increase of the effective film thickness. A center pin placed at the center of the double-strip resonator is introduced to improve the implementation of the filter and the frequency response. A double-strip two-pole dual-mode square patch filter with a 5.0-GHz center frequency and 100-MHz bandwidth was designed. The filter was fabricated using YBa2Cu3Oy thin films on CeO2-buffered Al2O3 substrates. A three-dimensional electromagnetic simulator was used to design and investigate the filter. The measured frequency response of the filter was in reasonable agreement with the simulated one. The measured power-handling capability of the filter was more than 31 W (44.9 dBm) at 60 K.

Surface Resistance of YBCO Thin Films under High DC Magnetic Fields

We have studied the magnetic dependence of the surface resistance (Rs) of YBa2Cu3Oy (YBCO) thin films by changing the direction of an applied magnetic field by mean of a micriostrip line resonator method (MLRM). We measured Rs(0), Rs(90) and Rs(45) to which the direction of the applied magnetic field was respectively normal, parallel and at 45° to the film surface. In the low temperature region, (below 40 K), the Rs(0) had low magnetic dependence; however, the Rs(90) and Rs(45) had high magnetic dependence, even below 10 K. We examined the magnetic field dependence of Rs (90) and Rs(0) using the London equation, and found that Rs(90) in the higher temperature region could be mostly explained by the theory.

A Novel REBCO Wire Structure That Improves Coil Quality Factor in MHz Range and its Effect on Wireless Power Transfer Systems

We have developed a structure consisting of two conventional REBCO wires that increases the quality factor of coils, and have simulated its effect on to wireless power transfer (WPT) systems. The proposed structure is used to reduce the conductor loss of the Hastelloy substrate. The conductor losses of the skin effect of the wires were reduced by not using a copper stabilizer and a silver overlayer. We investigated the effect of embedding the proposed structure in styrene foam on the coil quality factor and found that the foam reduced the quality factor due to its dielectric loss. We fabricated several different wire type spiral coils embedded in styrene foam and measured their quality factor at 300 and 77 K. The quality factor of the coil using the proposed structure was about 3.2 times that of one using copper wire at 300 K. We also simulated the power transfer efficiency of a WPT system using two coils with different quality factors for different distances between the coils. Use of a high-quality factor coil enabled the system to achieve a longer transfer range.

HTS Filter with Dielectric Rods for Tuning the Center Frequency and Trimming the Passband ripple

Tuneable filters are one of the most essential microwave components for multiband communication systems due to their attractive features. In this study, we developed high-temperature superconducting (HTS) tuneable microstrip line hair-pin resonator filter with dielectric rods for tuning the center frequency and trimming the passband ripple simultaneously. Several dielectric rods are placed above the HTS filter, and the center frequency and passband ripple are controlled by changing the distance between the dielectric rods and the resonators. Two dielectric rods are used for each resonator; one is located on the center of the resonator for tuning the center frequency and trimming the pass-band ripple, and the other is located on the open end of the resonator to tune the center frequency. The filter was designed to have a center frequency of 1.4 GHz and a bandwidth of 28 MHz by using an electromagnetic simulator based on the moment method. The HTS filter was fabricated using double-sided YBa2Cu3Oy thin film on a 30×40×0.5 mm Al2O3 substrate. The dielectric rods with a dielectric constant of 39 were used. As a result, the tuning range of the filter was about 140 MHz while keeping the all most the same insertion loss with trimming. The measurement data after trimming and tuning have a good agreement with the design specifications.