Showing papers by "Raheel M. Hashmi published in 2019"
TL;DR: An operational perspective of recent advances fabrication methods for flexible antennas is presented, while analyzing the strengths and limitations of each in the microwave as well as millimeter-wave regions.
Abstract: Antennas are a vital component of the wireless body sensor networks devices. A wearable antenna in this system can be used as a communication component or energy harvester. This paper presents a detailed review to recent advances fabrication methods for flexible antennas. Such antennas, for any applications in wireless body sensor networks, have specific considerations such as flexibility, conformability, robustness, and ease of integration, as opposed to conventional antennas. In recent years, intriguing approaches have demonstrated antennas embroidered on fabrics, encapsulated in polymer composites, printed using inkjets on flexible laminates and a 3-D printer and, more interestingly, by injecting liquid metal in microchannels. This article presents an operational perspective of such advanced approaches and beyond, while analyzing the strengths and limitations of each in the microwave as well as millimeter-wave regions. Navigating through recent developments in each area, mechanical and electrical constitutive parameters are reviewed, and finally, some open challenges are presented as well for future research directions.
96 citations
TL;DR: The proposed realization method is much simpler and more cost-effective than the existing realization methods of transparent antennas, and the prototype fabricated from the selected composite materials is more flexible and robust in bending operations than other transparent antennas.
Abstract: In this paper, a detailed investigation of the realization of conformal wearable transparent antennas by integrating conductive mesh with polymer has been presented. The proposed realization method is much simpler and more cost-effective than the existing realization methods of transparent antennas, and the prototype fabricated from the selected composite materials is more flexible and robust in bending operations than other transparent antennas. In this paper, the mechanical, electrical, and optical characteristics of the proposed composite material have been investigated to analyze its suitability for transparent flexible antenna realization. For concept demonstration, a prototype of a dual-band antenna operating at 2.33–2.53 GHz and 4.7–5.6 GHz has been fabricated and tested. These frequencies cover both the instrument, scientific, and measurement (ISM) and the wireless local area network (WLAN) bands. Full ground plane is utilized in the antenna design for on-body operations. The suitability of the antenna for wearable applications has been investigated by measuring its performance under physical deformation and testing its performance on phantom. Next, the RF performance of the antenna has been improved by using two layers of conductor to form the radiating element. Although transparency is slightly compromised, the double-layer element improves the gain and efficiency of the antenna.
46 citations
TL;DR: In this article, a broadband low-profile partially reflecting superstrate (PRS)-based antenna is presented for 60 GHz applications, which exhibits a peak gain of 18.8 dBi with a 3 dB gain bandwidth of 16.7%.
Abstract: In this communication, a broadband low-profile partially reflecting superstrate (PRS)-based antenna is presented for 60 GHz applications. The PRS with an asymmetric pattern of circular metallic patches printed on one side of a thin dielectric slab improves the feed antenna gain from 6.5 to 18.5 dBi. A prototype antenna exhibits a peak gain of 18.8 dBi with a 3 dB gain bandwidth of 16.7%. Simulated and measured radiation patterns of the proposed antenna are highly directive toward broadside over a large operating bandwidth. The prototype antenna is well matched with a measured voltage standing wave ratio (VSWR) below 2 over a frequency range from 55.6 to 69.6 GHz, corresponding to a matching bandwidth of 22.4%. Fabrication limitations and assembly tolerances are also discussed. Overall, the prototype validates the high gain and wideband performance of the proposed antenna. The total area of the PRS is $5.2\lambda _{0}^{2}$ and the overall height of the antenna is only $0.66\lambda _{0}$ at the lowest operating frequency of 55.6 GHz.
26 citations
TL;DR: In this paper, an on-chip spherical dielectric resonator is integrated with a resonant cavity antenna, which resulted in high radiation efficiency and increased gain, reaching 17.8 and 18.4 dBi for V-band and W-band, respectively.
Abstract: This letter demonstrates a novel integration approach to design high gain chip-fed antennas in V -band and W -band. An on-chip spherical dielectric resonator is integrated with a resonant cavity antenna, which resulted in high radiation efficiency and increased gain. The proposed approach minimizes the use of chip area and provides several advantages, such as, low profile and ease of assembly in comparison to similar antennas, reaching 17.8 dBi and 18.4 dBi gain for V -band and W -band, respectively.
15 citations
TL;DR: It is demonstrated that the entire unlicensed 60 GHz frequency band can be covered using a dielectric based aperture type antenna, which is unprecedented relative to medium-to-high gain millimeter-wave printed antenna arrays, used for similar applications.
Abstract: In this paper, a low-profile broadband antenna is presented for 60 GHz applications. It is demonstrated that the entire unlicensed 60 GHz frequency band can be covered using a dielectric based aperture type antenna. The antenna consists of a single-layer dielectric superstrate and an aperture type feed, which are separated by an air-cavity. The diameter of the superstrate is 15 mm, which is $2.75\lambda _{0}$ at the lowest operating frequency of 55.2 GHz. The simulated total efficiency of the antenna is greater than 88% over the entire operating band (55.2 GHz-65 GHz), which is unprecedented relative to medium-to-high gain millimeter-wave printed antenna arrays, used for similar applications. A prototype antenna was constructed, which exhibits a measured peak gain of 19.5 dBi. This value remains greater than 17 dBi over the entire operating bandwidth. The measured 3-dB beamwidths of the proposed antenna remain between 16° to 20° in the E-plane and 19.5° to 25° in the H-plane, respectively. The proposed antenna provides broadside directed radiation patterns with cross-polarization in the order of −30 dB over the entire operating band.
11 citations
11 citations
03 Mar 2019
TL;DR: Performance analysis of compact on-body antennas over a female body phantom shows that these antennas have good performance and successfully communicate under various near-body scenarios.
Abstract: This paper presents performance analysis of compact on-body antennas over a female body phantom. These antennas are designed to operate in 2.4GHz industrial, scientific and medical (ISM) band. In the design process, full ground plane is used to minimize radiation towards the body as they are intended to operate in near-body scenarios for Wireless Body Area Networks (WBANs). They offer significant advantages of compactness, light weight, wide radiation pattern over the body surface to provide maximum coverage, and less sensitivity to the variation of the gap between the antenna and the human body. These advantages make them of high interest for on-body communications and wearable applications. Results show that these antennas have good performance and successfully communicate under various near-body scenarios.
6 citations
01 Sep 2019
TL;DR: A simple, low-profile pattern reconfigurable antenna with a full-ground plane operating at 5.8 GHz that presents monopole-like radiation patterns with the gain of 4.4 dB for maximum coverage on the body and can be directed to ± 16 degrees with an increased gain by toggling the stubs for the semidirectional patterns states.
Abstract: In this paper a simple, low-profile pattern reconfigurable antenna with a full-ground plane operating at 5.8 GHz is presented. The antenna consists of a centre-fed circular patch, and a parasitic ring surrounding it. The ring is loaded with a rectangular slot on each side of the patch, and switchable stubs are added in the centre of each slot. With all the stubs in on-state, the antenna presents monopole-like radiation patterns with the gain of 4.4 dB for maximum coverage on the body, whereas the pattern of the antenna can be directed to ± 16 degrees with an increased gain of 2.3 dB, by toggling the stubs for the semidirectional patterns states. Numerical studies are carried out using ANSYS HFSS and preliminary results are presented.
6 citations
Proceedings Article•
01 Mar 2019TL;DR: In this paper, the suitability and effectiveness of transparent conductive fabric for design and realization of transparent wearable antennas is studied, which is an effective alternative for the realization of flexible transparent antennas when embedded in polydimethylsiloxane (PDMS).
Abstract: In this paper the suitability and effectiveness of transparent conductive fabric for design and realization of transparent wearable antennas is studied. In contrast to the other expensive and non-flexible transparent conducting materials, transparent conductive fabric is an effective alternative for the realization of flexible transparent antennas. When embedded in polydimethylsiloxane (PDMS) this fabric becomes mechanically robust against repeated bending which is a requirement for many wearable devices. The performance of the transparent conductive fabric embedded in PDMS is evaluated for the wearable antenna application by fabricating a simple patch antenna operating at 2.45 GHz and testing its performance. The antenna prototype has been fabricated by using transparent conductive fabric VeilShield to form the conducting parts including the radiating element and PDMS as the substrate and encapsulation. Experimental investigations of the antenna demonstrate the applicability of the proposed material for the realization of transparent wearable antenna through a simple and inexpensive fabrication process.
4 citations
07 Jul 2019
TL;DR: In this paper, a pathfinder beam reconfigurable antenna system for mm-wave applications is presented, which is completely passive and can provide continuous three-dimensional beam scanning in a conical region of ±40° from boresight direction.
Abstract: This paper presents the performance of a pathfinder beam reconfigurable antenna system for mm-wave applications. The system is completely passive and can provide continuous three-dimensional beam scanning in a conical region of ±40° from boresight direction. It uses a pair of near-field dielectric structures, inspired from optical prisms, introducing a pre-calculated phase gradient to the incoming wave front from a source antenna, and redirecting the radiated beam to an arbitrary direction with in a conical region with an apex angle of 80°. The proposed system can provide a peak gain of 20.7 dBi and does not require expensive phase shifters and a power distribution network.
2 citations
01 Sep 2019
TL;DR: In this paper, a 3D printed phase transformation lattice structure with two different arrangements of the unit cells is designed above the RCA at the one-eighth of wavelength, which exhibits a more uniform field distribution than that of the circular arrangement.
Abstract: Near field phase transformation lattice structure is presented to correct the electric field phase variation above a source antenna. A high gain resonant cavity antenna (RCA) is used as a source, which operates at 12 GHz. The 3D printed phase transformation structure, with two different arrangements of the unit cells, is designed above the RCA at the one-eighth of wavelength. The rectangular arrangement exhibits a more uniform field distribution than that of the circular arrangement. Additionally, in the rectangular arrangement, the gain of the antenna is enhanced by 2.11dB from 21.98 to 24.09 dBi, whereas in the circular arrangement, this value increased by 2.08 dB from 21.98 to 24.06 dBi. For both the cases, the aperture efficiency and bandwidth aperture efficiency product (BAEP) increased from 34.24 to 55.78% and 55.024 to 109.33%2, respectively.
01 Jul 2019
TL;DR: In this paper, a switchable frequency selective surface (FSS) based on composite flexible substrate has been investigated, which bends E-field and H-field directions over various bending curvatures and the corresponding behavior is analyzed.
Abstract: In this paper presents a switchable frequency selective surface (FSS) based on composite flexible substrate has been investigated. To make the FSS switchable, various combinations of switches are used. The design is bent E-field and H-field directions over various bending curvatures and the corresponding behavior is analyzed. It is observed that design has less variation when bending is applied along H-field direction. Whereas, slight variations are observed when bending is applied along the E-field direction. It is noted that the design exhibits stop band and pass band characteristics. Furthermore, in pass band it provides single wideband and dual band operations. These characteristics are preserved when bending is applied, thus making it suitable for wearable applications and modern communication systems.
01 May 2019
TL;DR: In this paper, the authors presented the designs and measurements of two compact single-layer all-dielectric resonant-cavity antennas (RCAs) with a measured peak directivity of 20.7 dBi and 3dB directivity bandwidth of 55.9%.
Abstract: This paper presents the designs and measurements of two compact single-layer all-dielectric resonant-cavity antennas (RCAs). Both the antennas are compact (footprint 0 ) and low in profile (overall height 0 ). The first RCA consists of a single-layer partially reflecting superstrate (PRS) in which thickness and permittivity vary from the center towards the edge of the PRS. Four commercially available dielectric materials are used to achieve this permittivity variation. This RCA demonstrates a measured peak directivity of 20.7 dBi and its 3dB directivity bandwidth extends from 12.75-19 GHz, which is 57% at the center frequency. The second RCA, made out of a single dielectric material demonstrates a measured peak directivity of 20.3 dBi and its measured 3dB directivity bandwidth is 55.9%. This class of compact single-layer RCAs, with a directivity bandwidth product per unit area (DBP/A) of greater than 1200, successfully overcomes the trade-off between directivity, bandwidth, profile and footprint and breaks the challenging barrier that has existed for RCAs over the last decade (and other planar high-gain antennas).
07 Jul 2019
TL;DR: In this article, two array topologies (comprising square and radial configurations) made out of a Transverse Permittivity Gradient Superstrate (TPGS) are investigated for meeting ETSI Class-2 specifications.
Abstract: Dense, wideband and high-gain Resonant Cavity Antenna Arrays (RCAAs) are presented in this paper. Two array topologies (comprising square & radial configurations) made out of a Transverse Permittivity Gradient Superstrate (TPGS) are specifically investigated for meeting ETSI Class-2 specifications. Their boresight performance is characterized on the basis of peak directivity, 3dB directivity bandwidth, and most importantly the far-field radiation pattern envelope (RPE) masks. In comparison to a 9 × 9 square array, a radial array (having 91 elements) is shown to achieve the peak directivity of 37 dBi with a 3dB directivity bandwidth of more than 20%. In addition, the radial array demonstrated the potential of satisfying minimum ETSI Class-2 antenna requirements with appropriate RPEs up to 50° and SLLs as low as -17 dBi.
01 Sep 2019
TL;DR: In this article, the authors describe the use of time-resolved microwave conductivity (TRMC), which is an effective and contactless technique, to study the dynamics of charge carrier generation and recombination in thin film-based conductive media.
Abstract: Microwave probing can be used to study the charge carrier dynamics in photo-conductive materials. Such studies are of paramount importance considering the significant efforts dedicated towards photo-voltaic energy generation now-a-days. Contactless methods to quantify the generation of charge carriers in film-based materials, under the influence of light of varying intensity, are much needed to enable screening of such materials to identify the most promising candidates [1]. We describe the use of time-resolved microwave conductivity (TRMC), which is an effective and contactless technique, to study the dynamics of charge carrier generation and recombination in thin film-based conductive media. In this work, we present numerical simulations carried out in CST Microwave Studio, and a practical microwave probe setup, to extend the TRMC technique for enabling new measurement capabilities. Such microwave-based probe setup can be used in-line with bulk-fabrication processes for evaluating quality of thin-film organic photo voltaic materials in real time.
01 Sep 2019
TL;DR: In this article, a broadband RCA fed by a probe-fed microstrip patch, which is readily integrated with transceiver chips, exhibits a peak broadside gain of 19 dBi with a VSWR 2:1 bandwidth ranging from 57 GHz to beyond 70 GHz.
Abstract: This paper demonstrates the resonant cavity antenna's (RCA) integration capability with the millimeter-wave (mm-wave) transceiver chips. A broadband RCA fed by a probe-fed microstrip patch, which is readily integrated with transceiver chips, is designed at 60 GHz. It exhibits a peak broadside gain of 19 dBi with a VSWR 2:1 bandwidth ranging from 57 GHz to beyond 70 GHz. Radiation performance of the RCA fed by a traditional waveguide aperture is also presented to demonstrate the feasibility of the proposed RCA in mm-wave practical applications.