Recently, Unmanned Aerial Vehicles (UAVs) have been widely utilized for various industry applications, and it is expected to be one of the key elements in the next-generation mobile communication system. For the design and evaluation of the mobile communication system in the sky, the air-to-ground (A2G) propagation channel characteristics have been investigated by the UAV-based measurement systems. However, there is a measurement resolution issue due to the limitation of the UAV payload. In this paper, we propose the UAV-based virtual array channel sounding system in the 4.8 GHz band to solve this limitation. In our system, the channel data are continuously measured by the receiver, which is mounted on the UAV station, while the UAV station flies along the measurement course. The data are combined offline, and they are processed virtually as data of large array antenna for investigation of angular characteristics of the propagation channel. A great advantage of our system is to be able to configure an arbitrary virtual antenna array in the air. To mitigate the UAV position error, 3D UAV positions are tracked by laser equipment and used in the array signal processing. The experiment was conducted in an indoor workshop space in the 4.85 GHz band. The HPBW of the angular power spectrum was 3.2 deg., which was quite a sharp value in this frequency band. The azimuth angular and distance estimation errors of incident radio wave were approximately 0.1 deg. and 0.01 m. Future works will include conducting experiments in various radio propagation environments and analyzing more detailed channel characteristics.

MACKEY (Meta-surface inspired Antenna Chip developed by KIT EOE Laboratory) has been proposed as a functional compact antenna that is not affected by surrounding metals. Parallel placement of two MACKEYs has also been proposed for Wi-Fi 2GHz and Wi-Fi 5GHz bands. However, the MACKEY parallel arrangement type has a large width L and requires two feeding points to excite each patch. In this report, we present the analysis and measurements results of the miniaturized multi frequency MACKEY, which is a modification of the conventional type for Wi-Fi 2GHz and Wi-Fi 5GHz bands.

In next-generation mobile communications, the proactive use of millimeter-wave and terahertz-wave frequencies, which can secure a wide frequency bandwidth, is anticipated. The authors reported a measurement method using a rotating reflector antenna to realize high-speed direction-of-arrival (DOA) measurement by rotating a large-aperture antenna at these frequencies. The authors previous method adopted a circularly polarized antenna as the primary radiator to accommodate the polarization rotation of the antenna. However, this method had the issue of angular dependence in the angular profile. To solve this problem, this paper proposes a measurement method that uses an orthogonally polarized antenna as the primary radiator of a rotating reflector antenna for rotational measurements, and processes the acquired data offline. To confirm the effectiveness of the proposed method, a demonstration experiment is conducted in an anechoic chamber, and it is shown that an angular profile with less angular dependence can be obtained than using a circularly polarized antenna as the primary radiator. We also show that the proposed method is capable of fast DOA measurement.

We propose a three-dimensional balun with a balanced non-contact connector in this letter. Both measurement and simulation results show that the proposed connector has good reflection below -20dB and transmission of almost 0dB over a 14.6% fractional bandwidth in the 2GHz band.

Tiny radio-frequency identification (RFID) tags with a 1 mm square scale can be attached to small insects such as ants and used to detect their passage at RFID reader antennas in a laboratory arena. Although the movement paths of ants can be restricted inside a narrow tube, the ants pass through the tube in various postures. A single small coil antenna attached to the tube generates nulls, where the tags become unreadable due to specific tag orientations. This letter proposes a tag reading system with three antennas generating major magnetic field vectors in three orthogonal directions, to eliminate nulls within the tube, regardless of the tag orientation.

In this research, a high-precision positioning method for 5G group communication terminals based on the mMTC scenario is proposed. Group positioning extends the original positioning for a single terminal to positioning for multiple terminals simultaneously, utilizing the interaction information between terminals to optimize the positioning results by using the parallel chaotic stochastic resonance processing technique. On the basis of traditional single target positioning algorithms, the mMTC communication mode is effectively used to increase the positioning information between terminals and improve the average positioning accuracy of each communication terminal in the 5G cluster.

With the technology advances and implementation acceleration of medical digitization, more and more medical devices with radio frequency (RF) wireless communication capabilities are adopted in the hospitals for the conveniences and easily for the deployments. That causes the concerns on electromagnetic interference problem affecting medical safety seriously and should be considered carefully in reality. As an attractive technology, visible light communication (VLC) uses visible light offering illumination and communication at the same time. Compared with the traditional RF communication systems, VLC has significant advantages such as energy saving, easy deployment, no radio interference, electromagnetic compatibility and etc.. In this paper, the experiment utilizing VLC in the digital operating room to reduce electromagnetic interference is presented with implementation details on the test environment and both uplink and downlink hardware design and key parameters to support video/image transmission. The effectiveness of VLC system is verified to deploy in a real digital operating room and support in operation.

The Wigner-Ville distribution (WVD) is a high-resolution time-frequency analysis method. However, the discrete WVD (DWVD) has the problem of a narrow frequency observation range. This is because the time sampling of the symmetric instantaneous auto-correlation function (SIAF) changes simultaneously in the positive and negative directions. As a result, the sampling period of the SIAF in the case of DWVD is doubled and the frequency observation range is halved. Therefore, we propose a DWVD that does not narrow the frequency observation range. Specifically, when deriving the SIAF, in addition to the conventional sample that varies in both the positive and negative directions, we consider a sample averaged over two samples that vary only in the positive or negative direction. The proposed process allows the DWVD to be performed without halving the frequency observation range. However, this process causes a small aliasing component, which can be reduced by the use of window functions. This study will demonstrate this effect by using the proposed method for chirp waveforms.

Radar imaging technologies have been utilized to detect concealed hazardous materials for security screening in public facilities. We have developed a high-throughput walk-through and whole-body security screening system called Invisible Sensing (IVS) based on radar imaging and deep learning. In our previous work, we have demonstrated that the IVS system can detect guns and knives while subject persons walk through the system. This paper presents a newly developed function to detect explosives in radar images on the IVS system. Since most explosives have low reflectivity to microwaves, it is difficult to detect the shape of explosives in radar images. In contrast, the human body is highly reflective and visible in radar images. We propose a novel approach to detect low-reflective explosives in radar images by learning shadow features against the high-reflective human body background. We demonstrate that the proposed detection technique integrated into the IVS system achieved successful explosive detection performance in real time.

This paper presents a reflective metasurface designed for beam steering at 300 GHz. The metasurface uses an H-shaped structure as its unit cell to achieve desired reflection phases. A supercell, consisting of 16 unit cells, covers a complete reflection phase range of 360 degrees. To achieve a radiation pattern with the main beam directed at 30 degrees from the broadside direction, 28 supercells are fabricated on a grounded GaAs substrate of dimensions 4.4 mm × 4.4 mm. Full-wave simulations are conducted, demonstrating that the proposed metasurface achieves an overall gain of 10 dBi under a horn excitation. In addition, the radiation and transmission performance of the proposed metasurface over a long distance in a complex environment with multipath effects is proven to be effective. These results suggest that such metasurfaces have significant potential in THz applications.

Terahertz-wave sensing is expected to be used for high-resolution metal detection because of its broadband nature and object transparency. However, when terahertz-band near-field image sensing is conducted using array antennas, the amount of signal processing increases significantly with the resolution. We propose a low-complexity imaging algorithm that changes the sensing resolution adaptively according to the area where an object may exist without compromising the object detection capability. Experimental results using actual measured data show that the proposed method reduces the computational complexity to less than one-third of that of conventional linear interpolation methods without degrading the quality of the sensed image.

In recent years, cooperative automated driving, which shares information from in-vehicle and roadside sensors via communication technology, has gained attention. To share sensor information, methods using occupancy grid maps (OGMs) have been explored. However, when using roadside sensors to estimate OGMs, which are installed at higher elevations than in-vehicle sensors, the challenge arises of being unable to accurately recognize the road environment due to increased undetected areas. This study proposed a method to estimate OGMs using roadside LiDAR sensors, considering undetected areas. And the proposed method was demonstrated to accurately reflect the road environment in OGMs.