| Research Abstract |
In this research project, we make design, fabrication, and measurement of miniaturized, loss-low, and high-performance superconductor filters for possible applications to mobile communication systems. We develop also design methods for complicated multi-order filters with cross-couplings between resonators. Furthermore, we do some preliminary studies on the design theory and methods of ultra-wide band (UWB) filters and multi-band filters for future wireless communication systems.
First, characteristics of microstrip spiral resonators are investigated, and 3-10 order bandpass filters (BPFs) are developed with a midband frequency of 1.93GHz and a fractional bandwidth of 2%. The proposed filters are less than 1/10 in size compared with conventional layouts. The designed CT (cascaded trisection) type and CQ (cascaded quadruplet type filters having cross-couplings between non-adjacent resonators show quasi-elliptic function responses with very steep attenuations.
On the other hand, as filters
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using coplanar waveguide (CPW) structures require only single-side superconductor film compared with microstrip filters, much lower fabrication cost is expected. In this project, CPW interdigital BPFs and BPFs using CPW spiral resonators with a midband frequency of 5.0 GHz and a bandwidth of 160MHz, are designed, fabricated, and measured. In the passband, the measured insertion loss is about 0.12dB, and return loss about 20dB.
Next, equivalent circuits and design formulas for multiband filters using composite resonators that own multi-resonance properties are developed. Microstrip dual-band and tri-band BPFs are designed and tested, and desired filtering characteristics are realized. Moreover, a design method is developed for filters using composite resonators and step-impedance resonators to produce transmission zeros instead of the conventional approaches using cross-couplings. Examples of microstrip filters having sharp attenuations and wide stopbands are developed with expected frequency responses.
Finally, UWB filters covering 3.1-10.6GHz and UWB filters covering 22-29GHz are developed respectively, using microstrip step-impedance resonators and stub-loaded ring resonators. Good performance is obtained, and the FCC's limit and Japan's limit for low-band UWB applications are mostly met.
The research results are published in 38 papers and reports, including 5 journal papers, 9 papers in international symposium proceedings, and 24 technical reports in domestic conferences and meetings. Less
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