An ocean radar can retrieve information about surface currents and wave heights from the first- and second-order scattering caused by Bragg scattering. However, when the spectra of the first- and second-order scattering overlap with the signal from an aircraft target, accurately determining the first- and second-order scattering values becomes challenging. To effectively observe the ocean wave, it is necessary to suppress the aircraft target signal and to enhance the ocean wave signal. Conversely, for the multipurpose application of ocean radar, such as detecting moving targets like aircraft, the suppression of the ocean wave signal and enhancement of the aircraft target signal are required. This paper demonstrates, through experimental results, that polarimetric filtering can be applied in ocean radar to selectively enhance or suppress the desired signal.

This paper discusses the optimization effects of a transmitarray on a direction-of-arrival (DOA) estimation using the transmitarray and a single receiving antenna. The transmitarray consists of 1-bit elements with 0° and 180° transmission phases. The transmission phase distribution was optimized using a genetic algorithm and compared to a random distribution. The optimized transmitarray achieves a DOA estimation accuracy comparable to that of a conventional system using a 3-element linear array antenna. The root mean square error (RMSE) of the optimized system exhibits a decreasing trend as the signal-to-noise ratio (SNR) increases. Notably, at an SNR of 20 dB, the RMSE is 20° lower than that of the 3-element linear array antenna.

This paper presents an antenna design for indoor positioning systems with the Internet of Things (IoT). The problem of direction-finding using a small array antenna with IoT devices is discussed. Theoretical studies clarify the limitations and challenges of using a null to estimate locations accurately and reduce antenna size and cost. Most importantly, electronic null-steering causes fluctuation in null-forming accuracy due to amplitude errors in the antennas and feeding circuits. This article experimentally demonstrates that this deviation error is suppressed using two copper wires and a suitable feeding circuit. The methods are feasible for practice as complicated corrections, such as amplitude controlling or signal processing, are excluded. The prototype steers a null with an angular resolution better than 4° within ±60°, verifying the simulated results.

A vertically polarized horizontal-plane omnidirectional antenna with a circular waveguide bent TM₀₁ mode converter and an axisymmetric single reflector is designed and fabricated for the 150 GHz band. Determining a frequency range of 147.8 GHz to 170.0 GHz as the operational band, where the transmission coefficient ratio of the TE₁₁ mode to the TM₀₁ mode is less than 1/3 that in the designed mode converter, the realized gain is 2.2 dBi to 8.8 dBi, and the angular gain variation at the measured frequencies in the band is 4.9 dB at the maximum in the fabricated antenna

In this letter, the relationship between the amount of leaves and leaf attenuation was clarified. We conducted FDTD calculations and measurements for a tree species called Red Robin and within the frequency range of 2.4GHz to 15GHz. In addition, we confirmed that the amount of leaves is defined by the product of the density of leaves and the length of the propagation path within the leaf area. We also defined leaf attenuation per unit leaf volume as LAC (leaf attenuation coefficient) to use as an index to quantify the leaf attenuation and clarified its frequency characteristics.

Patch antennas have been drawn rich attention in wireless system because of their low-profile structure, low cost and ease of manufacture. This paper discusses characterization of m × n metasurface for patch antenna in terms of bandwidth enhancement. To clarify the principle of operation of the periodic part, we focused on magnetic currents. As a result, it is found that at the design frequency of the periodic structure, both the patch and the periodic structure radiate. It was also found that the effect of elements not adjacent to the driving element was greater, radiating out-of-phase components.

Leaky wave antenna using dielectric image line has attracted attention as base station antennas in the sub-millimeter wave band because it has high gain and can achieve cosec² pattern. However, the pattern is affected by the feeding system such as parallel plate. Therefore, we investigated ways to suppress the influence of the feeding system and achieve cosec² pattern by applying offsets to periodically arranged metal strips.

High angular resolution is required for millimeter-wave radar, which is currently being studied for application. One method for improving angular resolution is distributed Time Division Multiple Access (TDMA)-Multiple Input Multiple Output (MIMO) radar. In order to realize a distributed TDMA-MIMO radar using millimeter wave radar, it is necessary to use delay circuit with extremely high precision. Such high-precision timing control is difficult to achieve with millimeter waves, which makes distributed radar difficult to implement. In this letter, we propose a timing synchronization method based on the results of cross-correlation calculations, assuming that delay circuit with sufficient precision cannot be used due to cost and other reasons, and demonstrate its effectiveness through computer simulations and evaluations using experimental data.

This study considers the electromagnetic coupling between two Hertzian dipoles located in two- and three-dimensional free spaces. First, we briefly review the generalized kQ theory with respect to the reciprocal two-port impedance matrix. The kQ concept is then applied to a basic 2D problem, where a pair of Hertzian dipoles is sandwiched between infinitely wide parallel conductor plates. One dipole is excited by a sinusoidal current, and the other dipole observes the voltage induced across it. Solving a 2D Helmholtz equation yields kQ=√λ/d/π, where λ is the wavelength and d is the distance between the dipoles. Similarly, we apply the kQ theory to a 3D problem and obtain kQ=3λ/4πd. Because a Hertzian dipole is a building block for practical antennas, the results of this study will offer a theoretical foundation for developing various types of wireless power transfer systems.

Image overlay uplink screen camera communication consisting of a small display with LED backlight modulation and an indoor rolling shutter camera has been studied. A previous study demonstrated that image overlay QPSK was achieved by compensating pixel values of the overlaid image using dual cameras. However, even after the compensation, variation in the pixel values remained, making it difficult to realize further M-ary modulation. In this study, a compensation method taking both the overlaid image and backlight modulation into account is proposed. Constellation, error vector magnitude, and bit error rate for image overlay 16QAM are experimentally evaluated using dual cameras.

Aircraft localization systems that use time difference of arrival (TDOA) measurements, called wide-area multilateration (WAM) systems, have been deployed for air traffic control. Although WAM performs better than radar, it requires a large number of ground stations. A possible solution by which to reduce the number of stations is to obtain additional measurements, such as the angle of arrival (AOA) and barometric altitude. However, the feasibility of hybrid localization has not been experimentally proven. Therefore, this study presents an experiment on aircraft localization using TDOA, AOA, and barometric altitude measurements to demonstrate that aircraft localization at only two sites is possible.

Density evolution (DE) plays a fundamental role in the analysis of channel coding systems employing iterative decoding, and it is a valuable tool to design such systems. This letter discusses the implementation of DE for polar codes. In this letter, fast Fourier transform based methods are difficult to apply due to the difficulty in optimizing the parameters, and therefore, DE is performed using a Monte Carlo simulation. Finally, examples of the applications of this method are presented.

In recent years, wireless measurement methods in the near-field are developed for antenna performance evaluation. The phase measurement is difficult in near-field above the millimeter wave band, then a method to retrieve the phase using only amplitude information from a sampling plane is investigated. In this paper, we propose a method that utilizes only a single planar measurement as a faster and simpler phase retrieval method.

Satellite positioning has become accurate to the millimeter order with the use of carrier phase observation data for distance measurement, but one type of error namely multipath error remaines. In this research, as a preliminary step to reducing multipath errors using the data observed with an array antenna, we used a general-purpose receiver and the MUltiple SIgnal Classification (MUSIC) method to determine the direction of arrival of satellite signals. It was found that the direction of arrival of satellite signals can be estimated from pseudo carrier phase observation data using the MUSIC method.

We propose a detection method based on the Parzen window method to mitigate inter-symbol interference. This method selects a trained dataset based on the neighboring symbols, following a decision feedback approach. Simulation results show the proposed method achieved a 3.3 dB improvement in the Q value for a QPSK signal degraded by inter-symbol interference.

We propose and investigate an ultra-high splitting ratio passive optical network (PON) using a hollow core fiber (HCF). An HCF is used for one of the downstream link for power delivery through feeding light, which powers an optical amplifier for the upstream that improves uplink power budget. We perform simulations to evaluate the maximum splitting ratio of the proposed HCF-based PONs. We show that the proposed system can support up to 4096 users in 25Gbps non-return-to-zero (NRZ) intensity-modulation (IM) and direct detection (DD), as well as 1024 users in 25 Gbaud 16QAM transmission.