We investigated a proximity sensor technique based on changes of an antenna’s characteristics when objects such as human bodies are near the antenna. Conventionally, the difference of the return loss (DRL) has been the detection metric used for this method to detect the presence of a human body. Although the ability to detect both the presence and the distance to the body is desirable, the DRL is difficult to use for distance detection. Here, we consider a new detection metric for distance detection: the distance of the complex reflection coefficient (DRC). Finite-difference time-domain analyses and measurements were conducted to demonstrate the validity of this metric for distance detection.

This paper introduces a simple position tracking system using image processing technology to measure the uncertainty caused by antenna misalignment in the extrapolation method. The antenna alignment is tracked using a camera in the extrapolation process. The uncertainty caused by misalignment can be quantitatively evaluated in the measurement. By the single-antenna extrapolation method, the expanded uncertainty (k=2) of the DRGH was estimated to be from 0.63 to 0.85 dB over a frequency range from 1 to 18 GHz.

In this Letter, a reconfigurable reflectarray (RA) based on liquid crystal (LC) electric controlling property at Ka band is presented. The innovation focuses on measuring the phase steering ability of the whole LC RA with a structure of 4-finger under plane wave incidence and application on the actual scene, which can steer scattering wave to blind spots, not just play a role of EM launcher, but also an relay. Results show the LC RA can steer phase continuously to 213° with bias voltages and beam steering to different directions and different areas are achieved. This work introduces a LC RA as Reconfigurable Intelligent Surface (RIS) that can steer scattered beam to increase receiving power at spot, which can be an application of RIS on wireless communication.

In recent years, there has been a spurt of activities to explore the terahertz (THz) band comprising frequencies above 100 GHz to support high data rates and low latency applications. In this light, the current study presents an overview of a novel in-house channel sounder operating at 300 GHz followed by elaboration of a high-resolution double-directional channel measurement performed in an office environment. The letter validates the sounder, wherein the measurement accuracy is assessed by comparing the results from the campaign and ray-tracing (RT) simulation. The measurement system is expected to contribute to the advancement of THz communications research.

This letter proposes a design of an X-band multi-layered all-metallic slot array antenna with gratings loaded between parallel plates. Unlike the conventional structure with gratings loaded in parallel to the polarization direction to eliminate detrimental resonance in a 2×2-slot subarray, this design loads the gratings perpendicular to the polarization direction. Furthermore, short stubs along the polarization direction are proved necessary to facilitate the good performance of the subarray. The proposed 16×8-slot array demonstrates low-reflection, wide-band and high-efficiency characteristics in measurements.

This letter describes a wideband circularly polarized (CP) array antenna with 2 × 2 alignment of sequentially rotated CP patch elements. Each patch element has a diamond-shaped artificial ground structure (DAGS), which extend the 3-dB axial ratio (AR) bandwidth of a CP antenna, and the patch elements in the array are fed with relative phases of 0°, 90°, 180° and 270°. The main purpose of this work is to show the potential of the 3-dB AR bandwidth by a combination of the DAGS and the sequential rotation technique considering the effect of coupling with neighboring elements. The proposed array antenna achieves an overlapped bandwidth of 74.9% (4.30 GHz-9.45 GHz) with the -10-dB |S₁₁|, 3-dB AR and 3-dB gain characteristics. Also, the 3-dB gain bandwidth of this antenna is 54.65% at 5.0 GHz-8.76 GHz. Furthermore, the cross-polarization is sufficiently suppressed in the main beam of 14 dBic. As a result, it is shown that the patch antenna with DAGS can be applied to sequential array technology with sufficiently low coupling, and the AR bandwidth can be broadened.

In this paper, the author described the examination results of interference suppression between mobile terminals using space diversity and Eigen-beamforming techniques of mobile terminals for millimeter-wave full-duplex MIMO systems. The system studied a method of simultaneously transmitting and receiving a signal on the same frequency band in uplink and downlink between a base station and a mobile terminal. Applying the space diversity technique to the mobile terminal when performing Eigen beamforming achieved further interference suppression. A ray-tracing simulation of millimeter-wave radio propagation in an outdoor environment confirmed this method’s effectiveness.

As the 6th generation mobile communication system is expected to use the terahertz wave band, it is essential to clarify the human body blocking and scattering characteristics as many small cells for indoor and outdoor use will be needed. In addition, since it is important to use high-gain antennas with orthogonal polarization to realize efficient MIMO transmission, it is necessary to clarify the polarization characteristics of human body blocking and scattering. Experiments conducted to investigate human body scattering in the terahertz wave band show that the scattering characteristics are polarization dependent.

In this letter, a method for path loss prediction in outdoor urban environments based on computer graphics technologies is presented. Each wall of buildings in an evaluation area is assigned to a different RGB color. We create two types of color images that are viewed from a transmission point (Tx) and receiving points (Rxs). By analyzing and comparing the colors of these images, the visible colors existed in both images corresponding to the single scattering walls are detected all at once. The numbers of pixels of the visible colors are used to calculate received powers of the single scattering waves. The average and RMSE of difference between predicted path loss results and measurement results are small with -0.5dB and 7.6dB, respectively. The computation time is extremely short.

Spatially selective modulation (SSM) is a physical layer security technique that uses multiple transmitting antennas and a single receiving antenna. SSM allows only the legitimate receiver to receive the desired modulated signal correctly because of the location dependence of a multipath channel. Previous SSM studies have been statistically conducted using the Rayleigh fading channel. Here, we evaluated the secret transmission performance of SSM using ray-tracing, which is a deterministic propagation model. We assumed an indoor environment in the evaluation. We found that increasing the separation between the transmitting antenna elements improved the secret transmission performance of SSM in the assumed environment.

In this paper, a novel dual-polarized microstrip array antenna is proposed and its characterisitics are investigated. In general, dual-polarized array antennas have complicated antenna element excitation methods and feeding circuits. Both-sided microwave-integrated circuit (MIC) technology such as a magic-T can simplify the antenna structure. As the proposed dual-polarized microstrip array antenna integrates magic-Ts, array elements and two orthogonal feed circuits can be arrenged on a single-layer substrate. The characteristics of the antenna are simulated and the results are compared with experimental values.

This paper reports on a coil structure that reduces magnetic fields formed in the surrounding area by providing a parasitic loop element with added parallel resonance circuit around the inner exited coil. It was shown that magnetic field strength can be reduced by approximately 30dB by superposition of the magnetic fields formed by currents flowing in the inner coil and the parasitic loop element. It was also shown that, by matching the resonance frequency of the parallel resonance circuit with the power transfer frequency, it is possible to suppress degradation of power transfer efficiency due to installation of the parasitic loop element.

While the use of unmanned aerial vehicles (UAVs) is increasing in various fields, small fixed-wing UAVs are expected to be utilized in applications such as transportation, large area observation and wireless relay station because of its long flight duration. Breguet’s equation is generally used as an estimation formula of the duration. However, data of the specific fuel consumption to be used in the formula are most uncertain for small-fixed UAVs, which weigh from several to 10kg. Therefore, this paper at first proposes the method to specify the specific fuel consumption from engine data sheet as well as propeller characteristics as to incorporate the rate into the duration estimation formula, and then describes its validity by flight experiments for small fixed-wing UAVs.

Real-time kinematic - global navigation satellite systems (RTK-GNSS) provide positions with centimeter error; however, performance in urban area is degraded by multipath error. Common approaches to mitigate multipath are satellite selection based on SNR values or classification of LOS and NLOS signals. In this study, carrier phase lock indicator and elapsed epoch when it is invalid was used to select satellites. Car experiment was done around Tokyo station for 1 hour. Results showed increased correct fix up to 273 epochs while wrong fix was maintained below 1% of the total fix data. Increased ratio values for ratio test were also observed.

This paper discusses a polling and scheduling method for UWB-based in-vehicle networks. In IEEE 802.15.4a/z, conveying as much sensor data as possible in a Physical layer Protocol Data Unit (PPDU) is more efficient. Therefore, this paper proposes a scheduling scheme that minimizes the number of frames to be transmitted by adjusting the readout phase of periodic sensor data. Compared to existing methods, our proposed method can aggregate sensor data into fewer frames, resulting in a decreased loss rate in our experiment.

In this letter, a compact and broadband printed monopole antenna for circular polarization is proposed. In order to reduce the antenna size and achieve the circular polarization, the ground plane is combined by two elliptical shaped conductors with different size, and the antenna is designed asymmetrically to the microstrip line. The simulated and measured bandwidth of the 10dB-return loss with a 3dB-axial ratio is 57.9% (2.65GHz-4.81GHz) and 52.0% (2.45GHz-4.17GHz). The size of the antenna is 0.178λ_c² (λ_c is a wavelength in free space at the center frequency).

In this study, we propose a structure that comprises both an electromagnetic wave absorber and antenna in the microwave band. The structure consists of a metallic patch layer at the top, dielectric layer in the middle, and slot layer at the bottom. The results demonstrate that the proposed structure is an electromagnetic wave absorber with a reflective property of -15 dB and an antenna gain of 4.8 dBi.

In this paper, we propose a visibility-aware 3D models transmission method for Virtual Reality applications. The proposed method dynamically adjusts the quality of individual models based on available network resource and their visibility to maximize user-perceived quality under delay constraints. Experiment results show that the proposed method can significantly improve the viewport quality compared to conventional methods.