Yuta Takagi

New CPW Quarter-Wavelength Resonator with Open Stubs for Multipole Dual-Band Bandpass Filter

This paper proposes a newly developed CPW quarter-wavelength resonator with open stubs for use in a multipole dual-band bandpass filter. The proposed resonator has odd- and even-mode resonant frequencies that are configured using the space between the center conductor and the open stubs. It is easy to configure independently the odd- and even-mode coupling coefficients because the two resonant modes have different current density distributions. We design and fabricate a four-pole Chebyshev 2.0-/3.5-GHz band bandpass filter to investigate the validity of the proposed resonator. The proposed resonator is suitable for use in a multipole dual-band bandpass filter.

Compact 2.4-/2.9-GHz band parallel-planar bandpass filter

This paper proposes a compact dual-band bandpass filter (DBPF) based on a parallel-planar architecture where resonators are formed on the opposite sides of each substrate. The proposed architecture enables dual-band operation without an appreciable change in the volume of the DBPF and yields design freedom for the resonant frequencies by adjusting the distance between the substrates. A 2.4-/2.9-GHz band DBPF is fabricated using YBCO film deposited on a MgO substrate with a coplanar waveguide structure to investigate experimentally dual-band operation. The measurement results agree with those of the simulation.

High-temperature superconducting coplanar-waveguide quarter-wavelength resonator with odd- and even-mode resonant frequencies for dual-band bandpass filter

This paper presents a high-temperature superconducting coplanar-waveguide quarter-wavelength resonator that has two different resonant modes for use in a dual-band bandpass filter (DBPF). An RF filter with multiple passbands such as the DBPF is a basic element that is expected to achieve broadband transmission by using separated frequency bands aggregately and simultaneously in future mobile communication systems. The proposed resonator has a folded center conductor and two open stubs that are aligned close to it. The odd- and even-mode resonant frequencies are configured using the space between the folded center conductor and the open stubs. It is easy to configure the odd- and even-mode coupling coefficients independently because the two resonant modes have different current density distributions. Consequently, a DBPF with two different bandwidths can be easily designed. This paper presents three design examples for a four-pole Chebyshev DBPF with different combinations of fractional bandwidths in order to investigate the validity of the proposed resonator. This paper also presents measured results of the DBPF based on the design examples from the standpoint of experimental investigation. The designed and measured frequency responses confirm that the proposed resonator is effective in achieving DBPFs not only with two of the same bandwidths but also with two different bandwidths.

Numerical estimation on intermodulation distortion of a high-temperature superconducting dual-band bandpass filter

This paper proposes a method that numerically estimates the intermodulation distortion (IMD) of a high-temperature superconducting (HTS) dual-band bandpass filter (DBPF) when two-tone signals are simultaneously input to each passband of the HTS-DBPF. The numerical estimation method is based on the third-order polynomial approximation of the input-output characteristics of the HTS-DBPF when a two-tone signal is input to each passband. To validate the proposed method, a 2.0-/3.5-GHz band HTS-DBPF is used to measure its IMD characteristics when two tones with a 30-kHz separation are individually and simultaneously input to each passband. The calculated and measured results confirm that the proposed method can be applied to estimate the IMD characteristics.

Compact 2.1/3.6 GHz Planar Bandpass Filter

This paper proposes a compact planar dual-band bandpass Alter (DBPF). The proposed DBPF employs a resonator comprising a combination of spiral and stepped-impedance structures in order to reduce the size of the DBPF. The feature of this filter is that these structures are placed close together to achieve a compact configuration. A 2.1/3.6 GHz superconducting planar bandpass filter is fabricated to investigate experimentally dual-band operation.