Kunihiro Kawai

Ring resonators for bandwidth and center frequency tunable filter

This paper presents a novel tunable resonator for a filter that independently changes its center frequency and bandwidth. The proposed resonator comprises a closed ring shaped transmission line with switches and three tunable reactive elements. The switches tune the frequencies at which transmission zeros appear (fzeros) and do not degrade the insertion loss at the resonant frequency (fr). The tunable reactive elements enable control of the fr. The prototype of the resonator is fabricated, and the measured characteristics demonstrate the feasibility of the proposed resonator. The fr of the resonator varies from 3.5 GHz to 5.1 GHz. A bandwidth tunable filter is also fabricated. Tuning range from 8% to 25% is obtained in the fractional bandwidth. These results approve the tuning of bandwidth by controlling fzeros.

Center Frequency and Bandwidth Tunable Filter Employing Tunable Comb-Shaped Transmission Line Resonators and J-inverters

This paper presents a novel and simple-structured digital tunable bandpass filter that individually controls the center frequency and bandwidth. The filter consists of tunable lambda/4-length resonators and tunable J-inverters. The employed tunable resonator has a transmission line with a comb-shaped pattern on both sides of the line and multiple switches placed between the teeth of the comb-shaped pattern. The tunable J-inverter comprises a microstrip gap having multiple conductor tips and switches in the gap. A prototype two-pole tunable bandpass filter is designed and fabricated to verify the feasibility of the proposed filter. The tuning ratios of the measured bandwidth and center frequency are 2.67 and 1.14, respectively

A high power and highly efficient multi-band power amplifier for mobile terminals

This paper presents a highly efficient multi-band heterojunction bipolar transistor power amplifier (PA) employing reconfigurable matching networks (MNs). The MN consists of field effect transistor switches and achieves the desired matching condition in the target frequency band by controlling the on/off status of switches. The fabricated reconfigurable PA has 3-stage and operates in 9 bands from 0.7 to 2.5 GHz, i.e., 0.7, 0.8, 0.9, 1.4, 1.7, 1.8, 1.9, 2.3, and 2.5-GHz bands, with over a 30 dB gain. It also achieves an output power of greater than 34 dBm and a power added efficiency of over 40% at the supply voltage of 3.5 V in each operating band.

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.

Reconfigurable RF Circuits for Future Band-Free Mobile Terminals

Reconfigurable radio frequency (RF) circuits will be the predominant solution for future global and compact mobile terminals. Recent progress in RF-microelectromechanical systems (MEMS) devices has bolstered the hope for the implementation of high-performance reconfigurable RF circuits. This paper presents configurations for a novel band-reconfigurable power amplifier, a reconfigurable isolator, and a center frequency and bandwidth tunable filter. These RF circuits were prototyped. The reconfigurable power amplifier using MEMS switches achieves comparable performance to that of a single-band power amplifier in four different frequency bands. The isolator and the filter prototypes confirm the feasibility of the proposed configuration. These reconfigurable RF circuits will contribute to band-free operation in future mobile terminals.

Tunable Ring Resonator Filter for Duplexer

This paper proposes a novel ring resonator filter that has tunable capabilities for the center frequency, bandwidth, and out-of-band characteristic. The filter comprises ring resonators, switches, and tunable reactive elements such as varactors and tunable stubs. The newly proposed ring resonator incorporates varactors and switches that are connected to tunable elements. The varactors are used to change the center frequency. The point of the proposed filter is that the bandwidth can be varied without varying the center frequency, and the tunable elements make the skirt characteristics near the center frequency to be asymmetric with respect to the center frequency, which is suitable for constructing duplexers.

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.

Reconfigurable amplifier towards enhanced selectivity of future multi-band mobile terminals

A single-path configuration and use of single-band devices with distributed reconfigurable matching networks have the potential to achieve the optimum RF front-end for future multi-band mobile terminals. Considering the difficulties in configuring a practical tunable filter as a top filter, collaboration between the filter and low-noise amplifier (LNA) is a candidate to achieve the performance level required for the RF front-end. More precisely, the LNA should have high selectivity against undesired out-of-band signals, and the selectivity should be tunable. As the first step, this paper presents a reconfigurable amplifier that incorporates integrated matching networks with MEMS switches. The fabricated amplifier that can change the frequency response exhibits an advantage through measurement with an out-of-band signal.

MEMS-based Reconfigurable RF Front-end Architecture for Future Band-free Mobile Terminals

A novel reconfigurable RF front-end architecture for future band-free mobile terminals is proposed. A single-path configuration and the use of single-band devices with distributed reconfigurable matching networks have the potential to achieve the optimum RF front-end for the transmission side. As the first step in verifying the proposed architecture, a reconfigurable quad-band power amplifier (PA) module is also presented. The 1W-class PA module using microelectromechanical systems switches and low temperature co-fired ceramic technology achieves the maximum power added efficiency of greater than 44% in the 0.9, 1.5, 2.0, and 2.6-GHz bands.

Compact 1.5GHz to 2.5GHz multi-band multi-mode power amplifier

This paper presents a compact multi-band/multi-mode power amplifier (PA) for mobile terminals. The PA is reconfigurable within the size of 6.2 x 8.05mm2 and covers the frequency bands for mobile communications from 1.5GHz to 2.5GHz. The experimental results in terms of gain, output power, and adjacent channel leakage ratio are very close to those of actually-used single-band PAs in mobile terminals. To the best of our knowledge, this is the first time that a compact PA is presented that is less than 50mm2 and covers the 1.5, 1.7, 1.8, 1.9, 2.3, and 2.5-GHz bands for GSM, W-CDMA, and LTE modes.