Hiroshi Okazaki

Bio: Hiroshi Okazaki is an academic researcher from NTT DoCoMo. The author has contributed to research in topics: Amplifier & Antenna (radio). The author has an hindex of 17, co-authored 115 publications receiving 946 citations. Previous affiliations of Hiroshi Okazaki include Nippon Telegraph and Telephone.

Quadrature hybrid circuit

Abstract: In a quadrature hybrid circuit which has first and second two-port circuits 11 and 12 inserted between I/O ports P 1 and P 2 and between I/O ports P 4 and P 3 , respectively, and third and fourth two-port circuits inserted between I/O ports P 1 and P 4 and between I/O ports P 2 and P 3 , respectively, and which is configured so that under the condition that the I/O ports P 1 to P 4 are matched, a high-frequency signal fed via the I/O port P 1 is divided between the I/O ports P 2 and P 3 and the divided two signals are output 90° out of phase with each other but no signal is provided to the I/O ports P 4 , there are provided SPST switches 7 and 8 responsive to external control to control electromagnetic connections or coupling across a plane of symmetry 5 of the quadrature hybrid circuit passing through intermediate points of symmetry 23 and 24 of the third and fourth two-port circuits 21 and 22.

Novel 900 MHz/1.9 GHz dual-mode power amplifier employing MEMS switches for optimum matching

Abstract: A novel scheme is proposed for a compact band-switchable power amplifier that employs Micro-Electro-Mechanical System (MEMS) switches in a matching network (MN). According to the on/off status, the switches change the frequency response of the MN, and then the optimum matching can be achieved in different frequency bands. Following the proposed scheme, a dual-band GaAs FET amplifier is designed for the 0.9-GHz and 1.9-GHz bands. The experimental results exhibit the small signal gain of greater than 16 dB and the saturated output power of 31 dBm in each frequency band with adequate efficiency. The performance levels are very close to those of single-mode power amplifiers employing the same FET.

Leakage power reduction apparatus

Abstract: A circulator extracts a transmission signal sent from a transmitter to antenna via the circulator and a duplexer, reflected by an antenna, and returned via the duplexer to the transmitter side The amplitude and phase of the extracted signal are adjusted by an amplitude-and-phase adjuster to generate an offset signal having the same amplitude and the opposite phase with respect to a leaking transmission signal included in a signal output from a third terminal of the duplexer when combined by a combiner The offset signal is combined in the combiner with the leaking transmission signal included in the signal output from the third terminal of the duplexer to suppress the leaking transmission signal

A 900/1500/2000-MHz triple-band reconfigurable power amplifier employing RF-MEMS switches

Abstract: A triple-band reconfigurable power amplifier (PA), which comprises the band-switchable matching networks with RF-MEMS switches, is presented. The design method of the triple-band PA is described and switch requirements for multi-band operation are discussed. The switch satisfies the estimated requirements. The fabricated triple-band PA achieves high output power and high power added efficiency in three different frequency bands, 900 MHz, 1500 MHz, and 2000 MHz, respectively. We conclude that the proposed reconfigurable PA is easily expanded to multi-band operation and is quite promising for future mobile terminals.

Matching circuit and multi-band amplifier

Abstract: A matching circuit includes a demultiplexer for demultiplexing a signal outputted from an amplification device into signals of respective frequency bands, and at least two matching blocks which are connected to the demultiplexer, are respectively fed with the signals of the respective frequency bands, and perform impedance matching in the respective frequency bands of the inputted signals. Impedance matching is performed on each of the demultiplexed signals of the respective frequency bands, thereby achieving a matching circuit capable of efficiently performing impedance matching in the respective frequency bands. With this matching circuit, it is possible to achieve a multi-band amplifier capable of simultaneously amplifying signals of multiple frequency bands with high efficiency and low noise.

Single channel full duplex wireless communications

Abstract: In one aspect there is provided a method. The method may include receiving a first analog radio frequency signal including a signal of interest and an interference signal caused by a second analog radio frequency signal transmitted in full duplex over a channel from which the first analog transmission is received; combining the first analog radio frequency signal and a portion of the second analog radio frequency signal to generate an output analog radio frequency signal characterized by at least a reduction or an elimination of the interference signal included in the output analog radio frequency signal; and providing the output analog radio frequency signal. Related apparatus, systems, methods, and articles are also described.

Tuning in to RF MEMS

Abstract: RF MEMS technology was initially developed as a replacement for GaAs HEMT switches and p-i-n diodes for low-loss switching networks and X-band to mm-wave phase shifters. However, we have found that its very low loss properties (high device Q), its simple microwave circuit model and zero power consumption, its high power (voltage/current) handling capabilities, and its very low distortion properties, all make it the ideal tuning device for reconfigurable filters, antennas and impedance matching networks. In fact, reconfigurable networks are currently being funded at the same level-if not higher-than RF MEMS phase shifters, and in our opinion, are much more challenging for high-Q designs.

Superconducting and normal state properties of Li 1+x Ti 2−x O 4 spinel compounds. I. Preparation, crystallography, superconducting properties, electrical resistivity, dielectric behavior, and magnetic susceptibility

Abstract: LiTi 2 O 4 is one end member of the homogeneity range of the spinel phase Li 1+x Ti 2−x O 4 (0≤x≤1/3) and is superconducting at temperatures up to 13.7 K. Various measurements were carried out in order to characterize the superconducting and normal state properties of LiTi 2 O 4 and of other compositions within the homogeneity range of the spinel phase. These measurements establish LiTi 2 O 4 as ad-band superconductor and show thatT c decreases to <1.5 K forx≳0.1. This disappearance of superconductivity with increasingx was found to be correlated with anomalous changes in the lattice parameter with composition, and, from electrical resistivity measurements, is tentatively attributed to the occurrence of a composition-induced metal-semiconductor transition atx≈0.1. The metallic character of LiTi 2 O 4 and the composition dependence of the observed electrical properties are shown to follow from crystallographic considerations.

The Audacity of Fiber-Wireless (FiWi) Networks

Abstract: A plethora of enabling optical and wireless technologies have been emerging that can be used to build future-proof bimodal fiber-wireless (FiWi) broadband access networks. After overviewing key enabling radio-over-fiber (RoF) and radio-and-fiber (R&F) technologies and briefly surveying the state of the art of FiWi networks, we introduce an Ethernet-based access-metro FiWi network, called SuperMAN, that integrates next-generation WiFi and WiMAX networks with WDM-enhanced EPON and RPR networks. Throughout the paper we pay close attention to the technical challenges and opportunities of FiWi networks, but also elaborate on their societal benefits and potential to shift the current research focus from optical-wireless networking to the exploitation of personal and in-home computing facilities to create new unforeseen services and applications as we are about to enter the Petabyte age.

Microwave resonator configured by composite right/left-handed meta-material and antenna apparatus provided with the microwave resonator

Abstract: A reflective impedance element is connected to a port of a composite right/left-handed transmission line, and operates at a predetermined operating frequency so that an impedance when the reflective impedance element is seen from the port becomes a pure imaginary number jB. A reflective impedance component is connected to a port of the composite right/left-handed transmission line, and operates at the predetermined operating frequency so that an impedance when the reflective impedance element is seen from the port becomes −jB.