S. Ono

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.

Power-handling Capability of Transmit Filters Using Superconducting Bulk Ring Resonators

The power-handling capability and frequency responses of superconducting bandpass filters (BPFs) at a center frequency around 5 GHz with a 100-MHz bandwidth were investigated for application to transmit filters. A 3-pole BPF was designed using a Chebyshev function with three pairs of the bulk ring resonators and the dielectric trimming rods with the same dimensions. Using this design, we simulated the frequency responses of the filter with low loss and passband ripple, and by adjusting positions of trimming rods a fine tuning of the filter responses was achieved. The BPF was fabricated using ring resonators made from a DyBa2Cu3Oy superconducting bulk and a pair of Al2O3 substrates in a Cu cavity with trimming mechanisms using dielectric rods. The filtering property with low insertion loss was clearly observed at 25 K. Power-handling capability of the 3-pole BPF of over 10 W (40 dBm) was observed.

Design for transmit bandpass filter and trimming method using superconducting bulk ring resonator and dielectric rods

We designed transmit bandpass filters (BPFs) by using superconducting bulk ring resonators and dielectric trimming rods at a 5.0 GHz center frequency with a 100 MHz bandwidth. The filter with ring resonators was smaller than the filter with disk resonators, where the size was defined as the distance between the input/output ports. We found that the size contributes significantly to the miniaturization of multi-pole filters. A trimming mechanism was also evaluated. The frequency shift region of a single ring resonator reached more than 500 MHz after we moved a dielectric rod whose dielectric constant was 39 into the ring resonator. A 3-pole strip-line BPF was also designed using a Chebyshev function by using three pairs of ring resonators and dielectric trimming rods with the same dimensions and by adjusting the positions of the trimming rods. We obtained the optimal frequency response with a low loss and passband ripple for this BPF.

Intrinsic Surface Resistance of YBCO Thin Films Under DC Magnetic Field

We investigated the dc magnetic field and temperature dependences of the microwave intrinsic surface resistance (<i>R</i>_s^int) of YBa₂Cu₃O_y (YBCO) superconducting thin films with various thicknesses. We used YBCO films from 100, 200, and 300 nm thick YBCO films deposited on CeO₂/Al₂O₃ substrates. The <i>R</i>_s^int is means the surface resistance of YBCO film without the dielectric loss of the substrates. The <i>R</i>_s^int was obtained from measured surface resistance (<i>R</i>_s) by using a phenomenological equation. The <i>R</i>_s was measured using the dielectric resonator method at 21.8 GHz. A dc magnetic field of up to 5.0 T was applied parallel to the c-axis of the superconducting thin films during the <i>R</i>_s measurements. The <i>R</i>_s^int of the YBCO thin films increased when the dc magnetic field was applied. These relations could be explained with the two-fluid model for high-frequency and high-magnetic field limits. The <i>R</i>_s^int ratio (defined as <i>R</i>_s^int (5T)/<i>R</i>_s^int (0T)) slightly decreased with the film thickness. These results indicate that the <i>R</i>_s^int of HTS films depends on the film thickness in the dc magnetic field and the <i>R</i>_s^int in a dc magnetic field may be related to the pinning center in the HTS films.

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.

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.

Development of High-Speed Mechanical Tuning System for HTS Filters

We developed a high-speed ( ~1 second) mechanical tuning system for HTS microstrip line (MSL) filters using a dielectric tuning plate, dielectric trimming rods, and conducting trimming rods. The tuning plate has windows through which the dielectric and conducting trimming rods pass. It was designed for a 3-pole filter with 5 GHz center frequency (fc) and 100 MHz bandwidth (BW) using a 3-dimensional electromagnetic simulator. The simulation of 500 MHz frequency shift induced by dielectric tuning plate was done and, in addition, by using both kinds of trimming rods an improvement of insertion loss (IL), pass-band ripples reduction and increase of bandwidth was achieved. In the experiment, the positions of the plate and the rods above the filter were adjusted by using high-resolution operating at room temperature step motors. The minimum step of moving the plate and the rods was 0.001 mm. We found that the fc was shifted by 500 MHz while retaining the IL, pass-band ripple, and BW by experimental evaluation. The time taken by the 500 MHz tuning was less than 1 second. These results indicate that our method and system will be useful for the next generation of wireless communication systems.

Improvement in Power-Handling Capability of Superconducting Filters Using Multi-Layered Microstrip Line Resonators

We investigated the power-handling capability of superconducting filters using multi-layered microstrip line resonators (MSLRs). A multi-layered MSLR consists of superconducting/insulating/superconducting multi-layered film to improve the power-handling capability of the superconducting filter. The current flowing along the bottom edges of the multi-layered MSLR was less concentrated than that in the conventional MSLR. A 3-pole filter using a straight-type MSLR was designed based on the Chebyshev function to have a center frequency of 5 GHz and a bandwidth of 100 MHz. The single-layered and multi-layered MSLR filters were fabricated with the simulated filter design using NbN single-sided 600-nm thick film and NbN/AlN/NbN single-sided 300/20/300-nm multi-layered film on MgO substrates. Both filters showed good frequency responses at 6.8 K. The input-output relations of both filters at 6.8 K were measured. The power-handling capability of the multi-layered MSLR filter was 1.9 dB larger than that of the single-layered MSLR filter. Thus, the multi-layered MSLR helped to improve the power-handling capability of superconducting filters.

A simple tuning method for high-temperature superconductor microstrip filters by using two dielectric floating plates

Frequency tuning is essential for quality control of high-temperature superconductor (HTS) filters for mobile communications. We demonstrate a simple tuning method that enables a ~500?MHz (~10%) shift of the center frequency of a three-pole microstrip filter with a small change in the bandwidth (~7%). Two dielectric plates placed above the filter structure were used for this purpose, with the dielectric constants of the two plates being 24 and 45, respectively. Simulated results obtained by using a full-wave electromagnetic analysis appeared to agree well with the measured values.