Wide Dual-Band Circularly Polarized Diecletric Resonator: Innovative Integration of a Single Hybrid Feed and Thin Grounded Metasurface.

This article presents an application of a grounded substrate-based metasurface for hosting dielectric resonators (DRs), enabling a wide dual-band circularly polarized (CP) operation. The antenna structure comprises centrally positioned rectangular DRs, one above the other, along with a 7 × 7 square-slotted metasurface. The metasurface and DRs are hosted above a grounded substrate, which is fed through a single coaxial feed placed at a specific angle, employing a modified upper probe of the coaxial feed. The proposed hybrid technique utilizes the combined benefits of the feed angle and a well-matched metasurface, resulting in performance improvement. Notably, a measured impedance bandwidth of 88.1% for |S11| is achieved within the frequency range of 4.0 GHz to 10.3 GHz. Furthermore, the antenna design exhibits two overlapping measured 3-dB axial ratio (AR) bandwidths: 23.62% from 4.25 GHz to 5.4 GHz and 5.12% from 7.6 GHz to 8 GHz. The peak gain of the antenna is measured at 8.4 dBic. Consequently, this innovative single-feed antenna design, characterized by its compact profile, holds significant potential for realizing multi-band operations. Furthermore, the developed antenna is well-suited for deployment in indoor radio links and INSAT applications.

Beam-Switching Antennas for 5G Millimeter-Wave Wireless Terminals.

Beam-switching is one of the paramount focuses of 28 GHz millimeter-wave 5G devices. In this paper, a one-dimensional (1D) pattern reconfigurable leaky-wave antenna (LWA) was investigated and developed for wireless terminals. In order to provide a cost-effective solution, a uniform half-width LWA was used. The 1D beam-switching LWA was designed using three feed points at three different positions; by selecting the feeds, the direction of the beam can be switched. The antenna can switch the beam in three different directions along the antenna axis, such as backward, broadside, and forward. The 1D beam-switching antenna was fabricated, and because of the wide beamwidth, the measured radiation patterns can fill 128∘ of space (3 dB coverage), from θ = -64∘ to +64∘ at ϕ = 0∘. Following this, two of these antennas were placed at right angles to each other to achieve two-directional (2D) beam switching. The 2D beam-switching antenna pair was also prototyped and tested after integrating them into the ground plane of a wireless device. The antenna is able to point the beam in five different directions; moreover, its beam covers 167∘ (θ = -89∘ to +78∘) at ϕ = 0∘, and 154∘ (θ = -72∘ to +82∘) at ϕ = 90∘.

Enhancement of Feed Source through Three Dimensional Printing.

The three-dimensional printed wideband prototype (WBP) was proposed, which is able to enhance the horn feed source by generating a more uniform phase distribution that is obtained after correcting aperture phase values. The noted phase variation obtained without the WBP was 163.65∘ for the horn source only, which was decreased to 19.68∘, obtained after the placement of the WBP at a λ/2 distance above the feed horn aperture. The corrected phase value was observed at 6.25 mm (0.25λ) above the top face of the WBP. The use of a five-layer cubic structure is able to generate the proposed WBP with dimensions of 105 mm × 105 mm × 37.5 mm (4.2λ× 4.2λ× 1.5λ), which can improve directivity and gain by 2.5 dB throughout the operating frequency range with a lower side lobe level. The overall dimension of the 3D printed horn was 98.5 mm × 75.6 mm × 192.6 mm (3.94λ× 3.02λ× 7.71λ), where the 100 % infill value was maintained. The horn was painted with a double layer of copper throughout its surface. In a design frequency of 12 GHz, the computed directivity, gain, side lobe level in H- and E- planes were 20.5 dB, 20.5 dB, -26.5 dB, and -12.4 dB with only a 3D printed horn case and, with the proposed prototype placed above this feed source, these values improved to 22.1 dB, 21.9 dB, -15.5 dB, and -17.5 dB, respectively. The realized WBP was 294 g and the overall system was 448 g in weight, which signifies a light weight condition. The measured return loss values were less than 2, which supports that the WBP has matching behavior over the operating frequency range.

Antennas for Licensed Shared Access in 5G Communications with LTE Mid- and High-Band Coverage.

Two novel antennas are presented for mobile devices to enable them to access both licensed shared access (LSA) bands (1452-1492 and 2300-2400 MHz) and all the long-term evolution (LTE) mid (1427-2690 MHz) and high (3400-3800 MHz) bands, together with the GSM1800, GSM1900, UMTS, and 3.3 GHz WiMAX bands. These antennas do not require any passive or active lumped elements for input impedance matching. One of them is a dual-band antenna and the other is a wideband antenna. Both antennas have high efficiency in all the LSA bands, as well as the mid- and high-LTE bands, and nearly omnidirectional radiation patterns in the mid band. In the high band, the radiation patterns of the wideband antenna are less directional than those of the dual-band antenna. The wideband antenna was fabricated and tested and the measurements demonstrated that it had good wideband performance in a wide frequency range from 1.37 to 4 GHz, covering all the above-mentioned bands.

Accurate optimization technique for phase-gradient metasurfaces used in compact near-field meta-steering systems.

Near-Field Meta-Steering (NFMS) is a constantly evolving and progressively emerging novel antenna beam-steering technology that involves an elegant assembly of a base antenna and a pair of Phase-Gradient Metasurfaces (PGMs) placed in the near-field region of the antenna aperture. The upper PGM in an NFMS system receives an oblique incidence from the lower PGM at all times, a fact that is ignored in the traditional design process of upper metasurfaces. This work proposes an accurate optimization method for metasurfaces in NFMS systems to reduce signal leakage by suppressing the grating lobes and side lobes that are innate artifacts of beam-steering. We detail the design and optimization approach for both upper and lower metasurface. Compared to the conventionally optimized compact 2D steering system, the proposed system exhibits higher directivity and lower side-lobe and grating lobe levels within the entire scanning range. The broadside directivity is 1.4 dB higher, and the side-lobe level is 4 dB lower in comparison. The beam-steering patterns for the proposed 2D compact design are experimentally validated, and the measured and predicted results are in excellent concurrence. The versatile compatibility of truncated PGMs with a low gain antenna makes it a compelling technology for wireless backhaul mesh networks and future antenna hardware.

Flexible and Transparent Circularly Polarized Patch Antenna for Reliable Unobtrusive Wearable Wireless Communications.

This paper presents a circularly polarized flexible and transparent circular patch antenna suitable for body-worn wireless-communications. Circular polarization is highly beneficial in wearable wireless communications, where antennas, as a key component of the RF front-end, operate in dynamic environments, such as the human body. The demonstrated antenna is realized with highly flexible, robust and transparent conductive-fabric-polymer composite. The performance of the explored flexible-transparent antenna is also compared with its non-transparent counterpart manufactured with non-transparent conductive fabric. This comparison further demonstrates the suitability of the proposed materials for the target unobtrusive wearable applications. Detailed numerical and experimental investigations are explored in this paper to verify the proposed design. Moreover, the compatibility of the antenna in wearable applications is evaluated by testing the performance on a forearm phantom and calculating the specific absorption rate (SAR).

A dielectric free near field phase transforming structure for wideband gain enhancement of antennas.

The gain of some aperture antennas can be significantly increased by making the antenna near-field phase distribution more uniform, using a phase-transformation structure. A novel dielectric-free phase transforming structure (DF-PTS) is presented in this paper for this purpose, and its ability to correct the aperture phase distribution of a resonant cavity antenna (RCA) over a much wider bandwidth is demonstrated. As opposed to printed multilayered metasurfaces, all the cells in crucial locations of the DF-PTS have a phase response that tracks the phase error of the RCA over a large bandwidth, and in addition have wideband transmission characteristics, resulting in a wideband antenna system. The new DF-PTS, made of three thin metal sheets each containing modified-eight-arm-asterisk-shaped slots, is significantly stronger than the previous DF-PTS, which requires thin and long metal interconnects between metal patches. The third advantage of the new DF-PTS is, all phase transformation cells in it are highly transparent, each with a transmission magnitude greater than - 1 dB at the design frequency, ensuring excellent phase correction with minimal effect on aperture amplitude distribution. With the DF-PTS, RCA gain increases to 20.1 dBi, which is significantly greater than its 10.7 dBi gain without the DF-PTS. The measured 10-dB return loss bandwidth and the 3-dB gain bandwidth of the RCA with DF-PTS are 46% and 12%, respectively.

All-metal wideband metasurface for near-field transformation of medium-to-high gain electromagnetic sources.

Electromagnetic (EM) metasurfaces are essential in a wide range of EM engineering applications, from incorporated into antenna designs to separate devices like radome. Near-field manipulators are a class of metasurfaces engineered to tailor an EM source's radiation patterns by manipulating its near-field components. They can be made of all-dielectric, hybrid, or all-metal materials; however, simultaneously delivering a set of desired specifications by an all-metal structure is more challenging due to limitations of a substrate-less configuration. The existing near-field phase manipulators have at least one of the following limitations; expensive dielectric-based prototyping, subject to ray tracing approximation and conditions, narrowband performance, costly manufacturing, and polarization dependence. In contrast, we propose an all-metal wideband phase correcting structure (AWPCS) with none of these limitations and is designed based on the relative phase error extracted by post-processing the actual near-field distributions of any EM sources. Hence, it is applicable to any antennas, including those that cannot be accurately analyzed with ray-tracing, particularly for near-field analysis. To experimentally verify the wideband performance of the AWPCS, a shortened horn antenna with a large apex angle and a non-uniform near-field phase distribution is used as an EM source for the AWPCS. The measured results verify a significant improvement in the antenna's aperture phase distribution in a large frequency band of 25%.

A Stripline-Based Planar Wideband Feed for High-Gain Antennas with Partially Reflecting Superstructure.

This paper presents a new planar feeding structure for wideband resonant-cavity antennas (RCAs). The feeding structure consists of two stacked dielectric slabs with an air-gap in between. A U-shaped slot, etched in the top metal-cladding over the upper dielectric slab, is fed by a planar stripline printed on the back side of the dielectric slab. The lower dielectric slab backed by a ground plane, is used to reduce back radiation. To validate the wideband performance of the new structure, in an RCA configuration, it was integrated with a wideband all-dielectric single-layer partially reflecting superstructure (PRS) with a transverse permittivity gradient (TPG). The single-layer RCA fed by the U-slot feeding structure demonstrated a peak directivity of 18.5 dBi with a 3 dB directivity bandwidth of 32%. An RCA prototype was fabricated and experimental results are presented.

Design, Modeling, and Evaluation of the Eddy Current Sensor Deeply Implanted in the Human Body.

Joint replacement surgeries have enabled motion for millions of people suffering from arthritis or grave injuries. However, over 10% of these surgeries are revision surgeries. We have first analyzed the data from the worldwide orthopedic registers and concluded that the micromotion of orthopedic implants is the major reason for revisions. Then, we propose the use of inductive eddy current sensors for in vivo micromotion detection of the order of tens of µ m. To design and evaluate its characteristics, we have developed efficient strategies for the accurate numerical simulation of eddy current sensors implanted in the human body. We present the response of the eddy current sensor as a function of its frequency and position based on the robust curve fit analysis. Sensitivity and Sensitivity Range parameters are defined for the present context and are evaluated. The proposed sensors are fabricated and tested in the bovine leg.

Reconfigurable antenna options for 2.45/5 GHz wireless body area networks in healthcare applications.

This paper presents electronically reconfigurable antenna options in healthcare applications. They are suitable for wireless body area network devices operating in the industrial, scientific, and medical (ISM) band at 2.45 GHz and IEEE 802.11 Wireless Local Area Network (WLAN) band at 5 GHz (5.15-5.35 GHz, 5.25-5.35 GHz). Two types of antennas are investigated: Antenna-I has a full ground plane and Antenna-II has a partial ground plane. The proposed antennas provide ISM operation in one mode while in another mode they support 5 GHz WLAN band. Their performance is assessed for body centric wireless communication using a simplified human body model. Antenna sensitivity to the gap between the antenna and the human body is investigated for both modes of each antenna. The proposed antennas exhibit a wide radiation pattern along the body surface to provide wide coverage and their small width (14 mm) makes them suitable for on-body communication in healthcare applications.

Layer-by-layer photonic crystal horn antenna.

We introduce a horn antenna in a three-dimensional layer-by-layer photonic crystal that provides highly efficient transmission from a defect waveguide to free space. This device is physically realizable, thus providing a significant advance over an ideal two-dimensional photonic crystal horn antenna. Through numerical simulations we demonstrate the directional nature of the radiation pattern in the H -plane and its broader radiation characteristics in the E -plane. The antenna is shown to achieve a bandwidth that is almost equal to that of the defect waveguide, which illustrates that this horn antenna operates as an excellent output coupler for the photonic crystal waveguide. Further, the horn antenna may be easily integrated with other layer-by-layer photonic crystal components to form ultracompact devices for communication systems.

Photonic crystal horn and array antennas.

We introduce a defect-based horn antenna in a two-dimensional photonic crystal. Our numerical simulations demonstrate the efficient, highly directional nature of the antenna. It has a large operating bandwidth, low loss, and an operating frequency that is scalable to various regions of the electromagnetic spectrum. We also show that the photonic crystal horn antenna can be successfully used in an array configuration that uses a feed network made from photonic crystal waveguide circuits. The feed network and antennas have been integrated into a single photonic crystal device. This photonic crystal array antenna is shown to have high directivity and compact size while retaining the advantages of the photonic crystal horn antenna.