Karu Esselle

University of Technology Sydney | UTS · Faculty of Engineering and Information Technology

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 th...

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 a...

This paper presents a new type of beam-tilted circularly polarized (CP) radial line slot array (RLSA) antennas. When the conventional beam tilting method is applied to CP-RLSA antennas, the aperture efficiency of the antenna degrades significantly due to very sparse slots in some parts of the antenna. A new method is presented to prevent this, and...

A novel technique to design a low-cost Frequency-Selective Surface (FSS) bandpass filter is presented in this paper. Wideband polarization-independent FSS bandpass filters are predominantly made of multiple microwave dielectric substrates, or non-commercially available composite materials with or without active components, contributing to a very hi...

Geometry plays an important part in the characteristics of meta-cells used to design beam steering metasurfaces. One of the most desirable aspects of these cells is a large phase shift range that can be achieved with good transmission amplitude. However, the existing and most commonly used geometries for these cells are not able to produce a comple...

In this paper we present a shared-aperture polarisation reconfigurable microstrip array designed to resonate at 11.5 GHz with a gain bandwidth of 2 GHz (~17%). The polarisation reconfigurability (both linear and circular) is achieved using two orthogonal and independently-fed sub-arrays that are intertwined together on the same aperture. Each subar...

Geometry plays an important part in the characteristics of meta-cells used to design beam steering metasurfaces. One of the most desirable aspects of these cells is a large phase shift range that can be achieved with good transmission amplitude. However, the existing and most commonly used geometries for these cells are not able to produce a comple...

In this paper we present a shared-aperture polarisation reconfigurable microstrip array designed to resonate at 11.5 GHz with a gain bandwidth of 2 GHz (~17%). The polarisation reconfigurability (both linear and circular) is achieved using two orthogonal and independently-fed sub-arrays that are intertwined together on the same aperture. Each subar...

Environmental sensors have come a long way over the last decade, surged in variety and capabilities. Such growth was impossible without developing wireless technologies, particularly antennas, thanks to advanced numerical computation software and artificial intelligence (AI). Sensors have numerous applications in industrial environments for purpose...

The proliferation of low-earth orbit (LEO) satellites and the LEO satellite internet will be a game-changer for the low-latency high-speed global internet. While this new generation of the satellite internet in conjunction with fifth generation network (5G) and sixth generation network (6G) enabled emerging technologies, such as precision farming a...

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 a Near-Field Meta-Steering system receives an obliqu...

The paper presents a method to design beam-steering antennas using a pair of 3D printed perforated dielectric structures (PDSs) placed in the near-field region of a base antenna, which has a fixed beam. Detailed designs and quantitative comparison of two beam-steering antenna systems are presented. One antenna system has a conical horn antenna and...

This paper presents an evaluative summary of recently reported optimization methodologies for phase-gradient metasurface-based beam-steering systems. Based on the objective function, we classify them into two separate categories , namely, radiation pattern-based optimization and Floquet-mode-based optimization. Each of these is discussed briefly, f...

In this paper, a frequency reconfigurable, conformal, durable, optically transparent, and unidirectional antenna design is demonstrated for the first time. In the demonstrated design, continuous frequency tuning is achieved by integrating a varactor diode in a folded dipole radiator, which is backed by a water-filled reflector to produce unidirecti...

A continuous beam-steering solution for circularly polarized (CP) radial-line slot array (RLSA) antennas is presented and demonstrated with a fabricated prototype. The solution is based on the Near-Field Meta-Steering (NFMS) method, which is implemented through a pair of highly transmitting hybrid metasurfaces (HMs) that are placed above a high-gai...

In this paper, a new method to design an ultra-wideband beam-steering antenna system is presented. The system is completely passive and suitable for millimeter-wave applications, including some in defence, where both discrete and continuous beam-steering in two dimensions (elevation and azimuth) is required at a reasonably fast speed. The beam-stee...

This paper presents an evaluative summary of the optimization algorithms based methods reported to improve the efficiency of Near-Field Meta-Steering (NFMS) systems. These methods are classified into two categories based on their objective functions. The first category includes methods, which defined their objective function in terms of directivity...

In linearly polarized (LP) radial line slot arrays (RLSAs), reflection cancelling slots (RCSs) are used in addition to the radiating slots (RSs) to reduce the return loss. The densely populated slotted RLSA apertures present the challenge of avoiding physical overlap between the RCSs and RSs. A solution to displace RCSs from their optimal position...

In this paper, a new type of low-cost free-standing all-metal frequency selective surface (AM-FSS) is studied and presented. The AM-FSS is developed using an extremely thin sheet of metal having a total thickness of λ 0 /80, where λ 0 is the free-space wavelength at the operating frequency. The fundamental element of the AM-FSS is a square ring of...

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 resonan...

We investigate the aptness of various 4th order (90°) rotationally symmetric phase-transforming cells for the upper phase-gradient metasurface, which always receives an oblique incidence wave from the lower metasurface in a Near-Field Meta-Steering system. A comprehensive study on the behavior of various phase-transforming cells and corresponding s...

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-dielectr...

In this paper, a study has been devoted to design a water-based flexible, robust and transparent antenna having unidirectional radiation pattern. Simulation analysis is presented to exhibit the determining factors affecting antenna performance and further a method is demonstrated to improve the performance. The proposed antenna is designed by utili...

A new approach to significantly increase the uniformity in aperture phase distribution, through time synchronization in near-electric field, of circularly polarized (CP) antennas is presented. The method uses the phase of the CP electric field vectors, obtained through full-wave numerical simulations, and does not rely on any approximation such as...

Electromagnetic metasurfaces are planar two-dimensional metamaterials, typically of subwavelength thickness. Unit cell elements of different shapes have been widely explored, including electric and magnetic dipoles, patches, arbitrary geometries and pixelated surfaces. Although pixelated metasurfaces have a great advantage of geometric versatility,...

Phase-gradient metasurfaces, also known as phase-shifting surfaces, are used to steer the beam of medium-to-high gain antennas. Almost all such surfaces are made of cell elements that are similar in shape and only differ in dimensional parameters to achieve the required spatial phase gradient. A limitation of using the same geometry for the cell el...

Presents information on the APS society Distinguished Lecturer series

Radial line slot array (RLSA) antennas have attractive features such as high gain, high efficiency, and planar low profile, but their gain bandwidths have been limited to less than 10%. This paper presents a method to significantly increase the gain bandwidth of RLSAs to over 30%. The key to the method is the application of a non-uniform radial TEM...

In this paper, new designs of optically transparent wearable antennas have been presented. The explored antennas have the excellent features of high flexibility, small size, low specific absorption rate (SAR) and high optical transparency. The proposed antennas are realised by utilising highly flexible, optically transparent and low-cost materials....

Optically transparent flexible tag antennas are highly desired for some applications, where unobtrusiveness and capability of mounting on curved surfaces are required. On the other hand, circular polarization minimizes signal degradation due to polarization mismatch between the reader and tag antennas, thus ensuring good communication quality and a...

Presents the APS society vrtual Distinguished Lecturer series during the COVID-19 pandemic.

Reconfigurable antennas have gained tremendous interest owing to their multifunctional capabilities while adhering to minimalistic space requirements in ever-shrinking electronics platforms and devices. A stark increase in demand for flexible and conformal antennas in modern and emerging unobtrusive and space-limited electronic systems has led to t...

Presents information on the AP society Distinguished Lectures series.

This paper presents a unique dielectric-free cell configuration that is useful as a building block to design low-cost transparent phase-gradient metasurfaces required for antenna beam steering using both far-field and near-field methods. Each cell is made of a few thin metal sheets each having an asterisk-shaped slot. A phase variation of 360 degre...

Broadband antennas find many applications in modern communication systems, such as Wi-Fi, 5G and SatCom. Multiple competing optimization methods are available for the application to antenna design, while it would be preferable to know in advance if any method is superior. Here, an application of the cross-entropy method, along with particle swarm o...

Presents informatin on the AESS Distinguished Lecturers series.

Presents information on nominations for the AP-S Distinguished Lecturer nominations.

A method to realize low-cost, optically transparent, flexible and unidirectional antennas is presented in this paper. The key to the method is making a flexible transparent reflector made using a new method- injection of pure water into a flexible transparent cavity that is made out of Polydimethylsiloxane (PDMS) polymer and integrating the flexibl...

A 3D printed planar permittivity-gradient superstrate (PGS) is used to improve the directive radiation characteristics of a waveguide fed compact resonant-cavity antenna (C-RCA). Far-field directivity of classical uniform-superstrate based RCAs is limited due to non-uniform aperture phase distribution caused by even transmission through the superst...

One of the key challenges of the development of flexible and optically transparent antennas and sensors is the limited availability of the suitable materials. The traditional transparent conductors suffer from the drawback of instability in repeated bending and twisting and, thus, are not appropriate candidates for flexible transparent antenna deve...

This paper addresses a critical issue, which has been overlooked, in relation to the design of Phase Correcting Structures (PCSs) for Electromagnetic Bandgap (EBG) Resonator Antennas (ERAs). All previously proposed PCSs for ERAs are made either using several expensive Radio Frequency (RF) dielectric laminates, or thick and heavy dielectric material...

A highly directive fractal antenna with a novel shape is proposed in this paper. Finite Element Method based simulations were carried out on the first three iterations of a hexagonal fractal ring and the performance was measured in terms of the resonant behavior, directivity, radiation efficiency, current distribution, and radiation pattern. The se...

This paper presents a wideband beam-steering antenna system for high-mobility millimeter-wave (mm-wave) systems. It can provide both continuous and discrete beam steering in two dimensions (elevation and azimuth) at a speed that is sufficient for various applications including some in defence. The antenna is completely passive and beam steering is...

The paper presents a 3D printable porous superstrate (PS) to enhance directive radiation performance of low to medium gain antennas. The PS design process is based on theory of near-field phase correction. Transmission phase through PS is locally varied by changing sizes of perforations in different sections of the PS. The PS is designed for a reso...

Low-cost all-metal partially reflecting surface (AMPRS) based resonant-cavity antennas are presented in this paper. The AM PRSs are made by introducing square-shaped slots in a thin metallic sheet having moderate to high reflectivity ranging from -4.12 dB to -1.27 dB. An RCA designed using highly reflecting AM PRS has maximum directivity of 16.54 d...

A comparative analysis of two phase correcting structures (PCSs) is presented for an electromagnetic-bandgap resonator antenna (ERA). PCSs are made out of two distinct high and low permittivity materials i.e. Rogers O3010 and polylactic acid (PLA) respectively. Design and performance analysis is based on superstrate height profile, side-lobe levels...

A low-loss multifeed antenna with controlled polarization and beam-steering is presented. A low-profile resonant cavity antenna is fed by multiple spherical dielectric resonators, demonstrating its multifeed capabilities. Each of the dielectric resonators are themselves fed from four different sides by microstrip resonators on a planar circuit boar...

This article presents a method to produce a highly directive circularly polarized radiation beam (gain>35 dBi) from an all-metal circularly polarized radial-line slot array (RLSA) antenna. The antenna comprises a single-layer radial TEM waveguide, fully filled with air, formed between a metal ground plate and a parallel metal slotted sheet, leading...

An elegant combination of electric near-field phase transformation technique and electromagnetic-wave refraction, implemented through a pair of 3D printed dielectric structures, has been used to demonstrate a Ka-band beam-scanning antenna system. The system comprises a resonant-cavity antenna (RCA), which is used as a base antenna, a stepped dielec...