High-frequency characterization and delay-time analysis have been performed for a short channel AlGaN/GaN heterojunction FET. The fabricated device with a short gate length (Lg) of 0.07 µm exhibited an extrinsic current gain cutoff frequency of 81 GHz and a maximum frequency of oscillation of 190 GHz with a maximum stable gain (MSG) of 8.2 dB at 60 GHz. A new scheme for the delay-time analysis was proposed, in which the effects of rather large series resistance RS + RD are properly taken into account. By applying the new scheme to a device with Lg=0.25 µm, we obtained an effective high-field electron velocity of 1.75107 cm/s, which is consistent with our previous results calculated using Monte Carlo simulation.

High gain extinction ratio and stable control of the phase in phase sensitive amplification are fundamental to realize either phase regeneration or quadrature squeezing of phase modulated signals in an efficient and robust manner. In this paper, we show that a combination of our previously demonstrated “sideband-assisted” dual-pump phase sensitive amplifier with a gain extinction ratio of more than 25dB, and a phase-locked loop based stabilization technique, enable efficient QPSK quadrature squeezing. Its stable operation is exploited to realize phase de-multiplexing of QPSK signals into BPSK tributaries. The phase de-multiplexed signals are evaluated through measurement of constellation diagrams, eye diagrams and more importantly, BER curves. The de-multiplexed BPSK signals exhibited an OSNR penalty of less than 1dB compared to the back-to-back BPSK signals.

Based on a recent remarkable development of digital beamforming (DBF) antenna technologies, we propose a new concept of kaleidoscopic antenna, we call it "software antenna," which is a more general one extending DBF schemes. The software antenna instantly reconfigures itself adapting its software and hardware to changes in the radio-environment. To realize the software antenna, the development of high-speed reconfigurable FPGAs is indispensable. As an intelligent antenna, we believe the software antenna could play a key role in the days of software radio having a function of mobile computing.

This paper describes the innovation in single chip package design for mainframe computers coupled with major advances in "Controlled Collapse Chip Connection (C4)" technology, multilayer ceramic technology, and thin-film technology. C4 technology allows the LSI chips to be connected with high integration and high-performance. Applying C4 technology to chip-to-package and package-to-module interconnections provides a higher level of connection pads out from a small package. A new material 96.5 Sn/3.5 Ag for solder joints has been developed to facilitate reliable interconnection where thermal fatigue might have been a problem. The microstructure of a fractured surface and the estimation based on "Finite Element Method (FEM)" are correlated. New material and a process of mullite-glass has been developed to attain a thermal expansion coefficient close to that of silicon. The metallized ceramic technology for the mullite-glass can be applied to the substrate of LSI packages as well as multilayer ceramic multi-chip modules. Thin-film technology has been studied to form high-density wiring on package substrates. Using photolithography technique, it is possible to pattern pads accurately enough for connection to an LSI chip. The polyimide-Al combination can be patterned by subtractive technique using liquid etchants and sputtering. The via formation process is simplified using a photosensitive polyimide so that the fabrication process for multilayer wiring becomes suitable for mass production. Hitachi recently announced the HITAC M-880 Processor Unit which makes extensive use of these technologies. The general features of the LSI package "Micro Carrier for LSI Chip (MCC)" is also outlined.

To enhance the anti-fading technique of direct sequence code division multiple access (DS/CDMA) schemes in land mobile radio communication systems, a two-dimensional RAKE reception (2D-RAKE) scheme in beam space digital beam forming (BS-DBF) antenna configuration is proposed. The proposed scheme is applied to cellular base stations where the received signals in the reverse link are relieved from multipath fading by means of enhanced RAKE combining in spacial and temporal domains. Fundamental performance in the reverse link under multipath fading environments is investigated by computer simulation applying a wideband propagation channel model.

Indoor free space optical (FSO) communication technology that provides high-speed connectivity to edge users is expected to be introduced in the near future mobile communication system, where the silicon photonics solid-state beam scanning device is a promising tool because of its low cost, long-term reliability, and other beneficial properties. However, the current two-dimensional beam scanning devices using grating coupler arrays have difficulty in increasing the transmission capacity because of bandwidth regulation. To solve the problem, we have introduced a broadband surface optical coupler, “elephant coupler,” which has great potential for combining wavelength and spatial division multiplexing technologies into the beam scanning device, as an alternative to grating couplers. The prototype port-selective silicon beam scanning device fabricated using a 300 mm CMOS pilot line achieved broadband optical beam emission with a 1 dB-loss bandwidth of 40 nm and demonstrated beam scanning using an imaging lens. The device has also exhibited free-space signal transmission of non-return-to-zero on-off-keying signals at 10 Gbps over a wide wavelength range of 60 nm. In this paper, we present an overview of the developed beam scanning device. Furthermore, the theoretical design guidelines for indoor mobile FSO communication are discussed.

Wide deployment of artificial intelligence (AI) is inducing exponentially growing energy consumption. Traditional digital platforms are becoming difficult to fulfill such ever-growing demands on energy efficiency as well as computing latency, which necessitates the development of high efficiency analog hardware platforms for AI. Recently, optical and electrooptic hybrid computing is reactivated as a promising analog hardware alternative because it can accelerate the information processing in an energy-efficient way. Integrated photonic circuits offer such an analog hardware solution for implementing photonic AI and machine learning. For this purpose, we proposed a photonic analog of support vector machine and experimentally demonstrated low-latency and low-energy classification computing, which evidences the latency and energy advantages of optical analog computing over traditional digital computing. We also proposed an electrooptic Hopfield network for classifying and recognizing time-series data. This paper will review our work on implementing classification computing and Hopfield network by leveraging silicon photonic circuits.

This paper addresses onboard processing architecture employing direct regeneration. The advantage of direct regeneration is its hardware simplicity, even though the bit error rate performance is slightly inferior to that of demodulation-remodulation scheme with coherent detection. The channel filtering schemes as well as achievable capacities are examined by computer simulation. It is found that the system with direct regeneration has advantage in channel capacity and transmit earth station e.i.r.p. for small earth stations. A possible configuration of direct regeneration onboard in future satellite systems is proposed.

This paper theoretically analyzed the performance of the RAKE combining (in the time domain), maximal ratio combining (in the spatial domain), and two-dimensional RAKE combining (in the spatial and time domains) techniques for multipath fading environments, where multipath waves are distributed in the spatial and time domains. The analysis was based on a diversity combining technique that employed the eigenvalues of the covariance matrix between branch signals. It was found that the performance of the fading mitigation was normalized by the beamwidth of an array antenna, for various parameters such as the number of antenna elements, angular spread, and angle of arrival.

A software antenna, which will be a key device realizing flexible and highly reliable wireless communications systems, is inherently matched with software defined radios (SDR). In this paper, first, key technologies on the software antenna are introduced. The technologies contain i) how to recognize the radio environment, ii) how to determine the optimum adaptive signal processing algorithm, and iii) how to reconfigure the digital beamforming circuit. Then, an image of a software antenna with reconfigurable eigenvector-beamspace configuration is presented. Finally, by assuming various propagation conditions, performance of the software antenna in terms of algorithm diversity is demonstrated.