Bio: Hitoshi Hayashi is an academic researcher from Sophia University. The author has contributed to research in topics: Power dividers and directional couplers & Wilkinson power divider. The author has an hindex of 4, co-authored 39 publications receiving 59 citations.
••01 Oct 2014
TL;DR: Owing to its optimized tandem structure and inner-layer crossovers, for operating characteristics within the frequency range 440-760 MHz, the hybrid exhibits a power coupling of 3.5 ± 0.6 dB and return losses greater than 23 dB.
Abstract: This paper presents a tandem Lange 3-dB 90° hybrid. The hybrid consists of two 8.34-dB Lange couplers connected in tandem and is implemented on a 4-layer flame resistant laminate, composed of woven fiberglass cloth with an epoxy resin binder (FR4) substrate, by using inner-layer crossovers, instead of conventional bonded crossovers. Owing to its optimized tandem structure and inner-layer crossovers, for operating characteristics within the frequency range 440–760 MHz, the hybrid exhibits a power coupling of 3.5 ± 0.6 dB and return losses greater than 23 dB. Furthermore, isolation and phase difference between the output ports is greater than 29 dB and 90° ± 1°, respectively.
TL;DR: In this paper, the authors present the simulation and measurement results for a miniaturized rat-race hybrid using six lumped-element components, implemented on an FR4 substrate using chip inductors and chip capacitors.
Abstract: This letter presents the simulation and measurement results for a miniaturized rat-race hybrid using six lumped-element components. The hybrid was implemented on an FR4 substrate using chip inductors and chip capacitors. For the 530- to 620-MHz frequency range, the rat-race hybrid exhibited power splits of −3.4 ± 0.7 dB, return losses of >18 dB, an isolation between output ports of >24 dB, and errors in the desired relative phase difference between output ports of <5°. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1125–1128, 2016
••01 Feb 2017
TL;DR: This paper uses realistic wireless data from the IEEE International Conference on Data Mining dataset and Azure Machine Learning Studio to perform Bagging and shows that this can achieve a highly accurate location estimation.
Abstract: Indoor systems cannot obtain a precise estimate of the location, due to unstable signals. In this paper, we use realistic wireless data from the IEEE International Conference on Data Mining (ICDM) dataset and Azure Machine Learning Studio to perform Bagging (also called bootstrap aggregating). By using the machine leaning technique in the Azure Machine Learning Studio, we can obtain more than 69 percent precision in identifying the correct area among 247 areas with only 505 training data. This result is equivalent to the second place entry in the IEEE ICDM Data Mining Contest. We show that this can achieve a highly accurate location estimation.
••01 Feb 2019
TL;DR: This paper compares the performance of activation functions on a deep image prior with the standard rectified linear unit (ReLU), leaky rectifiedlinear unit (Leaky ReLU), and the randomized leaky Rectified Linear Unit (RReLU).
Abstract: In this paper, we compare the performance of activation functions on a deep image prior. The activation functions considered here are the standard rectified linear unit (ReLU), leaky rectified linear unit (Leaky ReLU), and the randomized leaky rectified linear unit (RReLU). We use these functions for denoising, super-resolution, and inpainting of the deep image prior. Our aim is to observe the effect of differences in the activation functions.
TL;DR: In this article, a novel fabrication of nanostructures of silver (Ag) germanium telluride (GeTe) at room temperature and the control of resistive switching using them was reported.
Abstract: We report on a novel fabrication of nanostructures of silver (Ag) germanium telluride (GeTe) at room temperature and the control of resistive switching using them. We systematically fabricated Ag seed nanoparticles of various sizes by thermal annealing and demonstrated that deposition of GeTe by RF sputtering onto the Ag seed nanoparticles spontaneously produced nanostructures including broccoli-like, hollow nanostructures comprised predominantly of nanocrystalline grains of Ag, Ag3Ge, Ag2Te, and Ag5Te3. The nanostructure shape and the constituent crystalline phases depend on the amount of Ag used for the seeds. The nanostructure formation followed nanoscale phase separation and crystallization into an unexpected phase from the phase diagram, including a metastable state. The structural changes were characteristic of the Ag nanoparticles; no significant structural changes occurred for GeTe deposition onto Ag films. As an application of the spontaneously formed nanostructures, we demonstrated a control resistive switching when a voltage was applied with a lateral Ag electrode pair deposited onto the top. We found that the Ag amount used for the seed formation determined the polarity of resistive switching and the SET/RESET voltages. By increasing the Ag amount, the resistive switching turned from the clockwise direction to the counter-clockwise direction, and the SET/RESET voltages were lowered.
TL;DR: In this article, the authors present an extensive review of the Butler Matrix (BM) based beamforming networks, and discuss which type of BM will be suitable for the phased array antenna (PAA) systems in the upcoming 5G and next-generation of B5G wireless systems.
Abstract: Due to the rapid development of wireless communication technologies, the number of wireless users are radically increasing. Currently, $\sim 23$ billion wireless devices are connected to the internet, and these numbers are expected to increase manifolds in the years to come. The technology growth of the fifth-generation (5G) wireless systems will be needed to meet this high demand of the network. 5G wireless systems offer data-rates of up to 10Gbps, 1-ms latency, and reduced power consumption. It is a known fact that 5G wireless systems will be exploiting beyond the presently used 3 GHz microwave and millimetre-wave (mm-wave) frequency bands. This is the primary driver in the development of the 5G wireless system. Multi-beam Phased array antenna (PAA) systems are typically used in the deployment of 5G systems for high-gain and directionality. In current 5G and future Beyond 5G (B5G) antenna array systems, beamforming networks (BFNs) such as the Butler Matrix (BM) will play a key role in achieving multi-beam characteristics. So, this paper presents an extensive review of the BM based BFNs, and discusses which type of BM will be suitable for the phased array antenna (PAA) systems in the upcoming 5G and next-generation of B5G wireless systems. Moreover, this paper also summarizes the different types of BM designs based on the number of layers. The BMs are classified into the bi-layer, tri-layer, and four-layer structures. It includes different techniques that have been used to solve the problem of crossing, narrow bandwidth, and size reduction of the BM. From the previous studies, it is found that most of the past research work was performed using the bi-layer BM system, whereas the difficult geometries like tri- and four-layer BM are avoided due to their complex fabrication process. It is also found in this paper that the metamaterial (MTM) based bi-layer BM achieves low insertion-loss and phase-error, excellent bandwidth and compact size, and good S-parameter performance, which makes them an ideal BFN candidate for the upcoming 5G and next-generation B5G systems.
TL;DR: This paper proposes a novel compact butler matrix with improved bandwidth based on open-circuit coupled-lines and interdigital capacitor unit-cell to develop composite right/left handed (CRLH) transmission-line (TL) metamaterial structure.
Abstract: This paper proposes a novel compact 4 × 4 butler matrix (BM) with improved bandwidth based on open-circuit coupled-lines and interdigital capacitor unit-cell to develop composite right/left handed (CRLH) transmission-line (TL) metamaterial structure. The BM is implemented by the combination of compact 3dB quadrature hybrid couplers, 0dB crossover and 45° phase shifter on a single FR4 substrate (er = 4.3 and h = 1.66 mm). The simulated and measured result shows that the return loss and isolation loss are better than 14 dB at all the ports, good insertion loss of -7 ± 2dB, which cover the frequency range of 3.2 GHz to 3.75 GHz. The phase difference of -45°, 135°, -135° and +45° are achieved with a maximum average phase tolerance of 5°. The overall dimension of the BM is 70mm × 73.7mm, which shows the compactness of the proposed design that is 75% size reduction and 8.2 times improvement in the bandwidth (550MHz) as compared to conventional BM. The CST microwave studio is used to design and perform the simulations. Additionally, the simulated and measured scattering parameters and phase differences show that they are in good agreement. This compact and improved bandwidth of the proposed BM is suitable for 5G antenna array beamforming network.
01 Jan 2004
TL;DR: In this paper, space filling curves have been used to realize a family of miniaturized hybrid couplers, and the performance of the proposed space-filling hybrids is as good as that of the corresponding conventional structures, and even better in some cases.
Abstract: In this paper, space-filling curves have been used to realize a family of miniaturized hybrids. The large surface area occupied by a conventional structure has been significantly reduced through the use of space-filling curves having the same electrical characteristics. Several space-filling curves have been studied and implemented in different designs. The second-iteration Moore rat-race coupler occupies only 12.6% of the conventional coupler's area, while the area of the second-iteration Sierpinski branch-line coupler is 24.7% of the conventional case. On the other hand, a nine-section Minkowski coupled-line balun is confined in 60% of the conventional balun's area. However, the effective size reduction depends on the used space-filling curve, compression ratio, and associated coupling between segments. The performance of the proposed space-filling hybrids is as good as that of the corresponding conventional structures, and even better in some cases. The design and simulation of the proposed space-filling hybrids have been performed using a moment-method-based full-wave electromagnetic simulator. Measurements of one fabricated coupler prototype are in good agreement with simulation results.
01 Feb 2019
TL;DR: A new smart parking system that prevents low-speed contact accidents by estimating availability of slots in the parking lot and the position of pedestrians and estimation accuracy of the pedestrian / driver position is proposed.
Abstract: In recent years, the number of casualties and injuries at intersections and roads has been decreasing due to wide spread of safe driving support systems, but the number of casualties and injuries due to low-speed traffic accidents in parking lots has not decreased. In the parking lot, it is necessary to drive while looking for an empty slot, which may result in contact accidents with pedestrians. Therefore, in this research, we propose a new smart parking system that prevents low-speed contact accidents by estimating availability of slots in the parking lot and the position of pedestrians. The proposed system attempts to estimate positions of user’s smartphones by deploying a small number of beacon devices on the parking lot, and by analyzing the radio wave intensity measured by the smartphones. In addition, estimation accuracy of the position of the pedestrian / driver is evaluated by experimental evaluation in a parking lot. Through the performance evaluation, estimation accuracy of the vehicle’s position to higher than 98%, and estimation accuracy of the pedestrian’s position is about 70%.