A monopole water antenna with a relative permittivity of 81 and a variable conductivity has been studied. Three issues are addressed in the paper. Firstly, the relationship between the conductivity and antenna radiation efficiency is investigated. Secondly, a new feeding design for the water antenna is proposed and a good return loss, radiation efficiency and radiation pattern are obtained. Thirdly, experiments are conducted in anechoic and reverberation chambers to evaluate its performance. Good agreements are achieved between the simulation and measurement results. With different conductivity, the antenna may be regarded as a dielectric resonant antenna, a conducting antenna or their combination. This type of antenna can be considered as an attractive alternative to conventional antenna for various applications.

This paper presents a thorough review of the main techniques used for wireless power transfer (WPT) in implantable medical devices (IMDs) with a specific focus on the techniques that employ implantable antennas for energy harvesting (electromagnetic (EM) WPT techniques). The techniques are first analysed and compared based on the IMD application, power transfer efficiency (PTE), transfer distance, implantation depth, implant size, operating frequency, and specific absorption rate (SAR). The study provides a critical analysis of the main WPT system’s as well as implantable antennas’ design parameters that control the PTE and hence the charging rate of the IMD. The investigated design parameters include the WPT TX-RX antennas’ gain, WPT-RX size, transfer distance, and the WPT TX-RX antennas’ alignment. Tutorial simulation examples are included to showcase the impact of these design parameters on the amount of power coupled to the IMD. The paper also discusses recent techniques used for improving the amount of power received by implantable antennas, and hence higher PTE and IMDs charging rate, namely, the use of implantable MIMO WPT-RX antennas to mitigate antennas misalignment and the use of metamaterial surfaces to focus the power emitted from WPT-TX antennas towards the implantable WPT-RX antennas. The findings and observations reported in this study serve as a valuable resource for designers and researchers to comprehend the effect of various WPT TX-RX antennas design parameters on PTE. The analysis and full-wave simulation examples, included in the paper, are shown very useful in understanding the challenges associated with WPT in IMDs and in proposing potential solutions.

This paper presents a very compact, wideband, and enhanced-gain antenna for 5G applications. A simple single-layer millimeter wave (mm-wave) metamaterial lens (meta-lens) is used to improve the gain, aperture efficiency, and gain bandwidth of a slotted-patch antenna over a wide range of frequencies from 25 GHz to 31 GHz. The lens exhibits a metamaterial negative refractive index behavior, which is attributed to a substantial gain enhancement of around 4–5 dBi over the whole band compared to the gain values of the slotted patch antenna alone. The lens’s unit cell comprises a simple single-layer split ring resonator (SRR) whose dimensions are carefully chosen to improve transmitted power and suppress absorbed and reflected power. The meta-lens consists of $8\times 8$ subwavelength SRR unit cells. Each cell has an area of $1.6\times 1.6$ mm2, it is located in the near-field region closely above a slotted patch antenna to produce a total antenna size of $12.8\times 12.8\times 7.27$ mm3 ( $1.2~\lambda \times 1.2~\lambda \times 0.68~\lambda $ , where $\lambda $ is the free space wavelength at 28 GHz). The maximum gain of the proposed antenna is 12.7 dBi, the 1 dB gain bandwidth is 18%, the maximum aperture efficiency is 92%, and the −10 dB impedance bandwidth (10 dB B.W.) is 17%. This excellent combination of essential metrics is hard to realize at mm-wave using narrowband antenna structures (microstrip patch antennas), and the aperture efficiency is the highest thus far for such a class of antennas.

It has been shown that the correlation between the radiation patterns of two antennas can be measured in a reverberation chamber (RC). In this paper, it is shown that the self-correlation coefficient of an antenna, defined as the correlation between the radiation pattern of an antenna under test (AUT) and a transformed version of itself, can also be measured in an RC. It is found that the 3-D radiation pattern of the AUT can be reconstructed from the measured self-correlation coefficient by using spherical wave decomposition. Moreover, the axial ratio of the AUT can also be measured efficiently in the RC, when the pattern is directional. Numerical simulations and measurements in the RC and in an anechoic chamber have been undertaken. Good agreement is obtained, which confirms the validity of the proposed method. Thus, this novel method can become a very useful, cost-effective, and efficient method for 3-D antenna radiation pattern measurement.

Water antennas are a special type of antennas and have attracted limited attention so far. In this study, a monopole water antenna with a dielectric layer is chosen as an example to study some less obvious characteristics of the water antenna. The resonant frequency, radiation efficiency and fractional bandwidth are of particular interest. Firstly, the effects of the dielectric layer between the water and the ground plane are studied. The results show that this layer has a crucial effect on the antenna resonant frequency and radiation efficiency. Secondly, the water with different conductivity is investigated. With different conductivity, the antenna may be regarded as a dielectric resonant antenna, a conducting antenna or their combination. Thirdly, a water antenna with a supporting structure is fabricated for validation. Measurements are conducted in an anechoic chamber and a reverberation chamber to evaluate its performance as a function of various parameters. Finally, the water temperature electromagnetic characteristics are investigated. Good agreements are achieved between the simulation and measurement results. It is shown that this type of antenna shows better performance than the conventional antenna in aspects such as broadband, cost, reconfigurability, transparency and it can be a promising candidate for a range of applications.

This letter presents a very simple low-profile and compact single-element two-port planar inverted-F antenna (PIFA) with applications in Wireless Local Area Networks (WLAN) and Long Term Evolution (LTE) bands. The two feeding plates are placed perpendicular to each other where polarization diversity is exploited due to the fact that the two ports are cross-polarized. To isolate the two feeding ports, a slot is etched on the ground plane. This single-element PIFA has a height of h=5 mm, which makes it suitable for handheld applications and covers a wide frequency band from around 2.1 to 2.9 GHz for dB, therefore having applications in WLAN (2.45 GHz) and LTE and Worldwide Interoperability for Microwave Access (WiMAX) band (2.5-2.7 GHz), and can be used as a 4G terminal antenna for diversity and multiple-input-multiple-output (MIMO) applications .