A dual-polarized Vivaldi antenna pair has been designed for use in a vehicle-to-anything (V2X) measurement facility. The operating bandwidth is from 560 MHz to 7.7 GHz (173% fractional bandwidth), covering all the existing V2X communication frequencies. The ultrawideband (UWB) property was achieved by integrating quarter-wave baluns at the feeding point of two orthogonally crossed Vivaldi antennas. The measured port isolation between the two antennas is better than -28 dB. The cross-polarization discrimination of better than 17.2 dB and antenna gain of up to 9.2 dB have also been realized across the whole bandwidth. Three of the designed antennas were mounted on a vehicle testing facility and were used to measure the radiation patterns of a roof-top shark antenna under four different V2X scenarios. That is, vehicle-to-pedestrian, vehicle-to-vehicle, and vehicle-to-infrastructure and vehicle-to-network. The results have also been presented in this communication.

To demonstrate that the silicone-based polymer polydimethylsiloxane (PDMS) is suitable as a substrate for flexible/wearable antennae and sensors, an investigation of its various properties was carried out. The substrate was first developed in compliance with the requirements, and then its anisotropy was investigated using an experimental bi-resonator approach. This material exhibited modest but discernible anisotropy, with values of ~6.2/25 % for the dielectric constant and loss tangent, respectively. Its anisotropic behavior was confirmed by a parallel dielectric constant (ε_par) ~2.717 and an evaluated perpendicular dielectric constant (ε_perp) ~2.570—ε_par > ε_perp by 5.7%. Temperature affected PDMS’s dielectric properties. Lastly, the simultaneous impact of bending and anisotropy of the flexible substrate PDMS on the resonance properties of planar structures was also addressed, and these had diametrically opposed effects. PDMS appears to be a good contender as a substrate for flexible/wearable antennae and sensors based on all experimental evaluations conducted for this research.

The brain-machine interface (BMI) is a new area of research and it is still in the development stage. The key component for the brain-machine interface is internal and external antennas. In this paper, we propose an implantable antenna for wireless brain signal sensing and monitoring using an inhomogeneous multi-layer model of the human head. A model with seven layers composed of skin, bone, fat, dura, cerebro spinal fluid (CSF), grey matter and white matter was adopted for our multi-layer model. The antenna was embedded below the bone and above the dura of the head phantom. Artificial tissue emulating (ATE) materials were fabricated in semi-solid form and measurement was carried out to check the permittivity and loss tangent of each semi-solid ATE. Implanted antennas for wireless brain signal monitoring data must be compact, lightweight and biocompatible. The proposed antenna was designed with Taconic RF-35 as the substrate with an overall size of 10 mm ×10 mm × 0.5 mm3. The proposed antenna has a -10 dB reflection bandwidth of 2.42-2.50 GHz and a gain of -25 dBi at the broadside direction. The top and bottom insulators with a thickness of 0.5 mm each were also designed with a Taconic RF-35 substrate. A good agreement between simulated and measured results was achieved for the proposed antenna for both in free space and inside of head phantom.

In this paper, we analyze the effects of textile weaving and finishing processes on the performance of textile-based wearable antennas. Several textile-based patch antennas operating at 2.4 GHz were designed and fabricated for evaluation. All of them had the same geometry comprising a 1-mm-thick felt substrate in the middle, and silver ink screen-printed polyester fabric as the ground and patch at the bottom and on top. However, polyester fabric, the bare textile material for the conductive ground and patch was subjected to different weaving and finishing (tentering, scouring, and calendering) processes. It was observed that the antenna resonant frequency, bandwidth, radiation efficiency, and peak gain were varied by these processes, although the antenna geometry and screen-printing method were identical to each other. The best antenna exhibits a peak gain of 5.2 dBi and a radiation efficiency of 42.4%, while the worst shows corresponding values of 4.17 dBi and 34.8%. This implies that the weaving and finishing processes considerably impact textile-based wearable antenna performances.

Inserting a suspended line is a widely used technique to reduce the envelope correlation coefficients (ECC) of multiple-input multiple-output (MIMO) antennas, but its ECC reduction mechanism has not been carefully investigated so far. In this paper, MIMO antenna pairs connected with different suspended lines were evaluated using a full-wave simulation and measurement results. We calculated the surface current density at the center of the suspended line inserted between the antenna elements and found that the derivative of the surface current density was closely related to the ECC values. Furthermore, parametric studies showed that the suspended line length determines the ECC reduction bandwidth of the MIMO antenna, and the antenna length controls the ECC minimum frequency point. These guidelines provide useful insights into designing a low ECC MIMO antenna employing a suspended line.