Daisuke Koizumi

Tunable resonator employing comb-shaped transmission line and switches

This paper presents a novel digital tunable resonator. It comprises a /spl lambda//4-length microstrip transmission line with a comb-shaped pattern on both sides of the line and multiple switches. Each switch is placed on the edge of two adjoining comb teeth to connect them to each other. The resonant frequency of the resonator can be changed by controlling the high frequency current path length using the switches. Electro-magnetic simulations are performed and the estimated tuning ratio is 22%. A prototype of the proposed resonator is fabricated to verify the feasibility, and the measured characteristics agree well with the simulated ones.

Cryogenic receiver front-end with sharp skirt characteristics

This paper presents an experimental cryogenic receiver front-end (CRFE) with sharp skirt characteristics for mobile base stations. The CRFE comprises a high-temperature superconducting filter, a cryogenic low-noise amplifier, and a highly reliable cryostat that is very compact. The major characteristics of the proposed CRFE measured at 70 K are a centre frequency of 1.95 GHz, passband width of 20 MHz, sharp selectivity of 20 dB/100 kHz, 1.4 dB ripple, 31.3 dB average passband gain, and average passband equivalent noise temperature of 47.9 K. The CRFE weighs 19 kg and occupies 35 l. Random failure of the cryostat is also evaluated by a continuous operation test using four identical ones simultaneously. The cryostat used in the CRFE has a high reliability level of over five years of continuous maintenance-free operation.

A Miniaturized High Temperature Superconducting Bandpass Filter Using CPW Quarter-Wavelength Spiral Resonators

A novel compact high temperature superconducting BPF is developed by using coplanar waveguide quarter-wavelength spiral resonators. The filter is a 5-pole Chebyshev BPF with a midband frequency of 5.0GHz and an equal-ripple fractional bandwidth of 3.2%. The CPW spiral resonator is made as small as 1.02times2.1mm2. As a result, the 5-pole filter occupies an area of only 7.65x2.11mm2, less than one-third that of a newly reported CPW interdigital filter. The filter is fabricated by using 0.5mum YBCO film deposited on an MgO substrate. No bond-wire air-bridges are used and no post-tuning is made in the experiment. The measured filtering characteristics agree well with EM simulations and show low passband insertion losses in spite of the small size of the 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.

A 5-GHz band coplanar-waveguide high temperature superconducting filter employing T-form open gap

This paper presents a coplanar-waveguide (CPW) high-temperature superconducting (HTS) filter that has a T-form open gap as an input/output coupling structure to reduce the fluctuation in filter characteristics caused by dimension errors originating from the manufacturing processes of the filter. Numerical and experimental investigations based on a 5-GHz band CPW HTS filter confirm that T-form structure suppresses the fluctuation to a level lower than the existing structure. The fabricated filter has a center frequency of 5.006 GHz, a 3.5% (175 MHz) equal ripple bandwidth, a 0.11-dB ripple, and a 0.11-dB average insertion loss, all measured at 60 K.

A novel compact high temperature superconducting CPW bandpass filter

A novel high temperature superconducting interdigital bandpass filter is proposed by using coplanar waveguide quarter-wavelength resonators. The CPW resonators are arranged in parallel, and consequently the filter becomes very compact. The filter is a 5-pole Chebyshev BPF with a midband frequency of 5.0GHz and an equal-ripple fractional bandwidth of 3.2%. It is fabricated using a YBCO film deposited on an MgO substrate. The measured filtering characteristics agree well with EM simulations and show a low insertion loss in spite of the small size of the filter.

Cryogenic Receiver Front-End for Mobile Base Stations

This paper presents the fundamental configuration and characteristics of an experimental cryogenic receiver front-end (CRFE) for the 2-GHz band mobile base stations. The CRFE comprises a high-temperature superconducting filter, a cryogenically-cooled low-noise amplifier, and a highly-reliable compact-sized cryocooler. Major characteristics of the proposed CRFE are a center frequency of 1.95 GHz, passband width of 20 MHz, sharp selectivity of 20 dB/100 kHz, 1.4-dB ripple, 31.3-dB average passband gain, and average passband equivalent noise temperature of 47.9 K, all measured at 70 K. The CRFE weighs 19 kilograms and occupies 35 liters. Random failure of the cryocooler is also evaluated by a continuous operation test using four identical ones simultaneously. The cryocooler used in the CRFE has a high reliability level of over five years of continuous maintenance-free operation.

A Novel Compact Eight-Pole HTS Bandpass Filter Employing CPW Quarter-Wavelength Symmetric Diverging Resonators

This paper presents a novel compact high temperature superconducting bandpass filter that employs coplanar-waveguide quarter-wavelength symmetric diverging resonators. The coplanar-waveguide symmetric diverging resonator has a structure in which the open side diverges and then is folded over several times symmetrically in order to shorten the overall length of the resonator. The proposed resonator is 2.4 mm or less in length for use in the 5-GHz band, whereas the conventional straight resonator is approximately 6.4 mm long. An eight-pole Chebyshev bandpass filter is designed using the proposed symmetric diverging resonators. The entire length of the eight-pole filter is 26 mm. The frequency response of the fabricated filter agrees well with electromagnetic simulation results, and achieves a degree of miniaturization of 50% or more compared to the conventional filter in which straight resonators are arranged serially

A Novel Compact HTS Interdigital Bandpass Filter Using CPW Quarter-Wavelength Resonators

A novel high temperature superconducting interdigital bandpass filter is proposed by using coplanar waveguide quarter-wavelength resonators. The CPW resonators are arranged in parallel, and consequently the filter becomes very compact. The filter is a 5-pole Chebyshev BPF with a midband frequency of 5.0 GHz and an equal-ripple fractional bandwidth of 3.2%. It is fabricated using a YBCO film deposited on an MgO substrate. The measured filtering characteristics agree well with EM simulations and show a low insertion loss in spite of the small size of the filter.

Compact HTS bandpass filter employing CPW quarter-wavelength resonators with strongly-coupled open stubs

This paper presents a novel compact high temperature superconducting (HTS) bandpass filter (BPF) that employs a newly developed miniaturized coplanar–waveguide (CPW) quarter–wavelength resonators with strongly–coupled open stubs. The proposed resonator has a structure in which the open stubs are aligned close to the center conductor of the resonator. This is because strongly–coupled resonators have widely–split resonant frequencies, and the lowest resonant frequency is employed as the fundamental resonant frequency of the resonator in order to achieve miniaturization. The proposed resonator is 1.7 mm or less in length for use in the 5–GHz band, whereas the conventional straight resonator is approximately 6.4 mm long. A four–pole Chebyshev HTS BPF is designed and fabricated using the proposed CPW resonators. The entire length of the proposed four–pole filter is 15 mm. The frequency response of the fabricated filter agrees well with the electromagnetic simulation results. The proposed filter achieves a size reduction of at least 50% compared to previously reported filters without any degradation in the frequency characteristics.