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This paper proposes a novel miniaturized rectangular loop antenna sensor consisting of a multiturn wire and a cuboid ferrite core. The lateral surface of the ferrite core is tightly wound by the multiturn wire. To verify its feasibility, the antenna sensor is fabricated, and the antenna factor (AF) levels are measured using the three-antenna method from the very low frequency (VLF) to the high-frequency (HF) bands. The measured AF levels are 31.8 dB (with a covering plastic case) and 33.1 dB (without a covering plastic case) at 30 kHz. In addition, the proposed antenna is employed in the shielding effectiveness measurement of a small commercial cabinet to observe its suitability for shielding effectiveness (SE) measurement of small shielding enclosures. The SE values averaged over the frequency range from 10 kHz to 3 MHz are 4.1 dB and 12 dB in the horizontal and vertical polarizations, respectively.

The plasmas (electrons and ions) in the inner magnetosphere have wide energy ranges from electron volts to mega-electron volts (MeV). These plasmas rotate around the Earth longitudinally due to the gradient and curvature of the geomagnetic field and by the co-rotation motion with timescales from several tens of hours to less than 10 min. They interact with plasma waves at frequencies of mHz to kHz mainly in the equatorial plane of the magnetosphere, obtain energies up to MeV, and are lost into the ionosphere. In order to provide the global distribution and quantitative evaluation of the dynamical variation of these plasmas and waves in the inner magnetosphere, the PWING project (study of dynamical variation of particles and waves in the inner magnetosphere using ground-based network observations, http://www.isee.nagoya-u.ac.jp/dimr/PWING/ ) has been carried out since April 2016. This paper describes the stations and instrumentation of the PWING project. We operate all-sky airglow/aurora imagers, 64-Hz sampling induction magnetometers, 40-kHz sampling loop antennas, and 64-Hz sampling riometers at eight stations at subauroral latitudes (~ 60° geomagnetic latitude) in the northern hemisphere, as well as 100-Hz sampling EMCCD cameras at three stations. These stations are distributed longitudinally in Canada, Iceland, Finland, Russia, and Alaska to obtain the longitudinal distribution of plasmas and waves in the inner magnetosphere. This PWING longitudinal network has been developed as a part of the ERG (Arase)-ground coordinated observation network. The ERG (Arase) satellite was launched on December 20, 2016, and has been in full operation since March 2017. We will combine these ground network observations with the ERG (Arase) satellite and global modeling studies. These comprehensive datasets will contribute to the investigation of dynamical variation of particles and waves in the inner magnetosphere, which is one of the most important research topics in recent space physics, and the outcome of our research will improve safe and secure use of geospace around the Earth.

In this paper layout of long detection range radio frequency identification tag antenna mountable on metallic surface is presented. This tag antenna layout consists of two non-connected L-shaped load bars and two sectorial patches electrically connected through seven pairs of vias and conducting rear-plane to form a loop antenna. This proposed tag antenna can be tuned in wide range for impedance matching and introduces circular polarization. The tag antenna characteristics are also measured on metal plate. The results show that maximum detection range of the specimen, placed on metallic plate found to be 8.4 ms. The measured 10 dB bandwidth of circular tag antenna is 17 MHz (906–923 MHz) with simulated 3 dB axial ratio bandwidth of 13 MHz. This circular tag antenna is simulated with 4 W EIRP reader.

We analyze three transmission-line antennas using the moment method. Each line antenna comprises a coplanar feed line, loops, and straight segments connecting the loops and feedline. First, we investigate bent and branched line antennas with loops on one side of the feedline. It is found that the segment length affects both the beam direction and axial ratio for the bent line antenna; in contrast, it only affects the branched line antenna’s axial ratio, resulting in a more straightforward design. Subsequently, the branched line antenna is modified with loops on both sides of the feedline to enhance the gain. It is observed that the antenna shows a gain enhancement of 2.0 dB, maintaining the same axial-ratio bandwidth as that of the original branched line antenna. The simulated results are validated by experimental work.

Human body tissues have a strong effect on the antenna operation in wireless body area networks (WBANs). In this study, the authors present the deep investigations of the effect of body tissue thicknesses on the performance of an ultra wideband (UWB) loop antenna by simulations when the antenna is operated on contact with tissues. The planar UWB loop antenna is designed for the examinations, which is targeted to be used in UWB WBAN applications. The effect of tissue thicknesses on the antenna performance is analysed and characterised in the terms of reflection coefficient S11, gain and total antenna efficiency, group delay, radiation patterns and specific absorption rate by simulations. A parametric layered human body tissue model with the frequency-dependent behaviour is exploited in the investigations. Further, the reflection coefficient of the presented antenna is measured in the different locations of the author's body. The main aim of these investigations is to demonstrate how the thickness of outermost body tissues affects the antenna performance.

This paper investigates the performance of a low-profile 8 × 8 multi-input-multi-output (MIMO) antenna with zero ground clearance, designed using an intelligent antenna recommender system. A dissimilar antenna pair is employed to achieve multi-band resonance and enhance isolation for sub-6G mobile communication. The primary antenna is a loop antenna resonating at n77, n79, and n46 bands, designed with the aid of a model developed using a support vector machine (SVM). The auxiliary antenna is a modified monopole resonating at n78 and n79 bands to minimize the antenna footprint on mobile devices. An eight-antenna MIMO array is fabricated, and measured results demonstrate that the proposed antenna has a reflection coefficient of less than − 10 dB at 3.5, 3.7, 4.5, and 5.2 GHz, with diversity gain and isolation greater than 9 dBi and 15 dB, respectively. SAR analysis conducted on a human head model shows a maximum SAR value of less than 1.6 W/kg at all sub-6G bands, compliant with FCC standards. The proposed MIMO antenna offers a viable solution, even when integrated with a battery and display, without occupying internal space within a mobile phone.

The paper studies the design of ultra-wideband printed loop antenna based on the characteristic mode manipulated in a large frequency band. The structure of this antenna is very simple. The wide impedance bandwidth of 60% with |S11| < –10 dB (2.76–5.16 GHz) is obtained due to a simultaneous excitation of the significant antenna modes. A stable radiation pattern is also achieved within the frequency bandwidth. The antenna is designed on FR4 substrate and fed with 50 Ω coupled tapered transmission line.

A flexible meandered loop antenna is proposed, designed and realised for small cylindrical implantable devices. This antenna covers the Medical Device Radiocommunications Service (MedRadio) and the 433–434 MHz industrial, scientific and medical (ISM) bands, and is probably the smallest reported flexible implantable antenna that covers these bands. This antenna has shown a robust performance in the presence of implant internal components and has a realised gain of − 28.4 dBi inside a model of a human upper arm.

Abstract—In this paper, a modified design of a planar square-loop antenna is presented for Electronic Article Surveillance (8.2 MHz) Radio Frequency Identification applications. The main purpose of the proposed design is to enhance the transmission efficiency of a loop antenna without disturbing other performance parameters. For that purpose, the spacing between the loop turns is adjusted in such a way that the coupling between similar loop antennas can be enhanced. Therefore, from measured results, it is observed that the proposed antenna provides a transmission efficiency of 63.92% at a center frequency of 8.198 MHz, and it also provides a –10 dB impedance bandwidth of 6 kHz.

Ionospheric clutter is one of the main problems for high-frequency surface wave radars (HFSWRs), as it severely interferes with sea surface state monitoring and target detection. Although a number of methods exist for ionospheric clutter suppression, most are suitable for radars with a large-sized array and are inefficient for small-aperture radars. In this study, we added an auxiliary crossed-loop antenna to the original compact radar antenna, and used an adaptive filter to suppress the ionospheric clutter. The experimental results of the HFSWRs data indicated that the suppression factor of the ionospheric clutter was up to 20 dB. Therefore, the Bragg peaks that were originally submerged by the ionospheric clutters could be recovered, and the gaps in the current maps can, to a large extent, be filled. For an oceanographic radar, the purpose of suppressing ionospheric clutter is to extract an accurate current speed; the radial current fields that were generated by our method showed an acceptable agreement with those generated by GlobCurrent data. This result supports the notion that the ionospheric suppression technique does not compromise the estimation of radial currents. The proposed method is particularly efficient for a compact HFSWRs, and can also be easily used in other types of antennas.