Karu P. Esselle

Bio: Karu P. Esselle is an academic researcher from University of Technology, Sydney. The author has contributed to research in topics: Antenna (radio) & Microstrip antenna. The author has an hindex of 46, co-authored 545 publications receiving 7875 citations. Previous affiliations of Karu P. Esselle include University of South Australia & University of Sydney.

The Use of Simple Thin Partially Reflective Surfaces With Positive Reflection Phase Gradients to Design Wideband, Low-Profile EBG Resonator Antennas

Abstract: Partially reflecting surfaces (PRS) with positive reflection phase gradients are investigated for the design of wideband, low-profile electromagnetic band gap (EBG) resonator antennas. Thin single-dielectric-slab PRSs with printed patterns on both sides are proposed to minimize the PRS thickness and to simplify fabrication. Three such surfaces, each with printed dipoles on both sides, have been designed to obtain different positive reflection phase gradients and reflection magnitude levels in the operating frequency bands. These surfaces, and the EBG resonator antennas formed from them, are analyzed theoretically and experimentally to highlight the design compromises involved and to reveal the relationships between the antenna peak gain, gain bandwidth, the reflection profile (i.e., positive phase gradient and magnitude) of the surface and the relative dimensions of dipoles. A small feed antenna, designed to operate in the cavity field environment, provides good impedance matching (|S11| <; -10 dB) across the operating frequency bands of all three EBG resonator antennas. Experimental results confirm the wideband performance of a simple, low-profile EBG resonator antenna. Its PRS thickness is only 1.6 mm, effective bandwidth is 12.6%, measured peak gain is 16.2 dBi at 11.5 GHz and 3 dB gain bandwidth is 15.7%.

A planar resonator antenna based on a woodpile EBG material

Abstract: A resonator antenna made from a complex artificial surface and a metallic ground plane is described. The complex surface is realized using a woodpile electromagnetic bandgap (EBG) material, which is shown to have a frequency dependent reflection plane location. A highly directive radiation pattern is created due to the angle-dependent attenuation of the resonator antenna coupling to free space. The antenna has the advantages of low height, low loss, and low sidelobes. It is shown that the directivity can be varied over a fixed range by changing the aperture size of the device, with the maximum directivity determined by both the feed element and EBG material properties. The complete bandgap for the woodpile EBG material is confirmed from a band diagram, and its properties as a complex surface are investigated through transmission calculation and measurement. The design of the antenna is described, and two means of exciting the resonator, a microstrip patch and a double slot, are investigated. Theoretical results for these two antennas are calculated the using finite-difference time-domain and are shown to be in good agreement with measured results.

A Single-Layer Frequency-Selective Surface for Ultrawideband Electromagnetic Shielding

Abstract: An efficient approach to achieve the shielding effectiveness (SE) by using a frequency-selective surface (FSS) is presented. This FSS, which consists of cross dipoles and rings printed on the opposite sides of a single-layer FR-4 substrate, exhibits a wide, 7.5-GHz stopband to provide simultaneous shielding in both X- and Ka-bands. Experimental results confirm SE of the prototype over an ultra-wide band with more than 20-dB measured attenuation. The design is compact and suitable to provide shielding against the radiation interference caused by license-free and other radio systems.

E-shaped patch antennas for high-speed wireless networks

Abstract: Thin, broad-band, E-shaped microstrip patch antennas (ESPAs), operating in the 5-6 GHz frequency range, are presented. They are intended for high-speed (IEEE 802.11a, 54 Mb/s) wireless computer local area networks (WLAN) and other wireless communication systems. They are suitable for WLAN adaptor cards in the PCMCIA (also known as PC) format, allowing users of current notebook computers to upgrade to this high-speed wireless standard at a low cost. Importantly, our antennas are thin enough to be accommodated in a PCMCIA card of standard 5-mm thickness, without making the antenna end thicker than the card itself. Two different closely spaced antenna pairs are also presented for diversity. A new ESPA configuration with a microstrip feed is presented for easy integration with microwave transceivers. In all cases, within the two IEEE 802.11a WLAN bands (5.15-5.35 GHz and 5.725-5.825 GHz), the reflection coefficient at the antenna input is <-10 dB and in both antenna pairs, mutual coupling between the two antennas is <-20 dB.

Steering the Beam of Medium-to-High Gain Antennas Using Near-Field Phase Transformation

Abstract: A method to steer the beam of aperture-type antennas is presented in this paper. Beam steering is achieved by transforming phase of the antenna near field using a pair of totally passive metasurfaces, which are located just above and parallel to the antenna. They are rotated independently or synchronously around the antenna axis. A prototype, with a peak gain of 19.4 dBi, demonstrated experimentally that the beam of a resonant cavity antenna can be steered to any direction within a large conical region (with an apex angle of 102°), with less than 3-dB gain variation, by simply turning the two metasurfaces without moving the antenna at all. Measured gain variation within a 92° cone is only 1.9 dBi. Contrary to conventional mechanical steering methods, such as moving reflector antennas with multiaxis rotary joints, the 3-D volume occupied by this antenna system does not change during beam steering. This advantage, together with its low profile, makes it a strong contender for space-limited applications where beam steering with active devices is not desirable due to cost, nonlinear distortion, limited power handling, sensitivity to temperature variations, radio frequency losses, or associated heating. This beam steering method using near-field phase transformation can also be applied to other aperture-type antennas and arrays with medium-to-high gains.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Photonic crystals

Abstract: The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

Dielectric Resonator Antennas

Abstract: Linearly and circularly polarized conformal strip-fed dielectric resonator antennas (DRAs) are studied in this article. In the latter case, a parasitic patch is used to excite a nearly degenerate mode. The hemispherical DRA, excited in its fundamental broadside TE111 mode, is used for the demonstration. In the analysis, the mode-matching method is used to obtain the Green's functions, whereas the method of moments is used to solve for the unknown strip currents. In order to solve the singularity problem of the Green's functions, a recurrence technique is used to evaluate the impedance integrals. This greatly increases the numerical efficiency. Measurements were carried out to verify the calculations, with good results. Keywords: circularly polarized antenna; dielectric antennas; mode-matching methods; moment methods; parasitic antennas; resonance

Infrared regulating smart window based on organic materials

Abstract: Windows are vital elements in the built environment that have a large impact on the energy consumption in indoor spaces, affecting heating and cooling and artificial lighting requirements. Moreover, they play an important role in sustaining human health and well-being. In this review, we discuss the next generation of smart windows based on organic materials which can change their properties by reflecting or transmitting excess solar energy (infrared radiation) in such a way that comfortable indoor temperatures can be maintained throughout the year. Moreover, we place emphasis on windows that maintain transparency in the visible region so that additional energy is not required to retain natural illumination. We discuss a number of ways to fabricate windows which remain as permanent infrared control elements throughout the year as well as windows which can alter transmission properties in presence of external stimuli like electric fields, temperature and incident light intensity. We also show the potential impact of these windows on energy saving in different climate conditions.