Y. Ranga

Enhanced gain UWB slot antenna with multilayer Frequency-Selective Surface reflector

Adequately design Frequency Selective Surfaces (FSSs) allow significant control of the phase of reflection and transmission characteristics over a wide frequency band. This property is used here to develop a multilayer FSS reflector enhancing the gain and radiation properties of antennas for ultra wideband applications. These kinds of reflectors make structures low profile by providing the flexibility in mounting them closer to antenna without disturbing the impedance bandwidth and providing a good gain control in the main beam direction. In order to design a suitable reflector dual layer FSS have been designed and employed with a slot antenna. FSS layer works from 4 GHz to 12 GHz, providing a linear transmission phase in the 133% bandwidth. Performance of the FSS is tested with UWB slot antenna and predicted results show significant gain enhancement while maintain the bandwidth of 140%.

Oblique incidence performance of UWB frequency selective surfaces for reflector applications

In this paper the response of a dual-layer, ultra wideband (UWB) frequency selective surface (FSS) reflector to obliquely incident electromagnetic waves is investigated. The results show a stable transmission response over an ultra-wide bandwidth for both transverse magnetic (TM) and transverse electric (TE) polarizations. Performance of the FSS is evaluated for incidence angles up to 50° with respect to the normal to the surface. The unit cell consists of a two-layer structure and possesses symmetry in two orthogonal planes. For 0° incidence, the designed FSS shows a linear phase response with a stop bandwidth greater than 100%. These printed FSS reflectors are highly suitable for use with planar UWB antennas, giving flexibility of mounting antennas close to conducting surfaces. They provide good isolation between the antennas and external conductors and minimize near field effects such as impedance mismatch.

Planar-Monopole-Fed, Surface-Mounted Quasi-TEM Horn Antenna for UWB Systems

A compact, quasi-TEM horn antenna is presented. This planar-monopole-fed, surface-mounted, UWB antenna has nearly constant gain of 4.8 ± 0.65 dBi from 2.75-12 GHz. It is λ/4 (45 mm) long at the lowest operating frequency. It also has nearly linear phase response in this ultrawideband. The radiation pattern in the azimuth plane is broad and the pattern in the elevation plane is relatively narrow.

Design and analysis of frequency-selective surfaces for ultrawideband applications

In this paper we investigate a multilayer frequency-selective surface (FSS) and its potential use in ultra wideband (UWB) antennas. A complete design and analysis of the FSS with an example UWB antenna is presented. The multilayer FSS provides an appropriate reflection phase to act as a reflector for the UWB antenna and is able to enhance its gain. A design guideline for the FSS is presented via a parametric study. Evaluation of the multilayer FSS with a UWB slot antenna shows a significant enhancement of gain across an ultra wideband (140%) impedance bandwidth. Its compact configuration provides flexibility for mounting the reflector close to the slot antenna geometry and makes it more suitable for various UWB devices. Simulations show a linear phase response across 4 to 12 GHz band which is sufficient for ultra wideband operation.

An extremely wideband printed antenna for wireless communication systems

A coplanar waveguide (CPW) fed semi circular disc antenna with a modified ground plane is presented. The proposed antenna consists of a semicircular radiating patch and semicircular arc-shaped ground plane. To achieve extremely wideband, two modifications are introduced. The first one is to modify the ground plane, and the second one is to insert slits near the feed point. Theoretical results show that the proposed antenna operates over 3.0 to 40 GHz for VSWR < 2. Details of the proposed antenna are presented, and simulated results show that the antenna has stable radiation patterns and good gain over its whole frequency band.

CPW-Fed semicircular slot antenna for UWB PCB applications

A coplanar wave guide (CPW) fed semicircular slot antenna (SSA) with step impedance transformer is presented. Omni-directional radiation pattern in whole band with theoretical gain of 3 dBi with variation of ±0.5 dB is achieved. It has shown that this design of SSA gives experimental bandwidth of 10.7 GHz for VSWR ≪2. Present results show suitability of structure for UWB communication.

Stretchable and highly conductive carbon nanotube-graphene hybrid yarns for wearable systems

Carbon Nanotubes (CNTs) have emerged as potential candidates for replacement of conventional metals due to their significant mechanical, electrical, thermal properties and non-oxidizing abilities [1, 2]. The density of CNT composites is about five times lower than copper and around half that of aluminium. Moreover, their thermal conductivity is about ten times that of copper. With the above mentioned distinguishing features, CNTs have been of interest in medical, electronics and antenna applications [3]. CNTs are drawn into yarns by pulling and twisting them from CNT forests. Previously we have presented microwave characterization of CNT yarns [4]. Our results have shown that the CNT yarns exhibits frequency independent resistive behavior and is beneficial for wideband applications such as ultra-wideband (UWB) and wireless body area networks [4]. Electrical conductivity of a CNT yarn depends on the properties, loading and aspect ratio of the CNTs. It also depends upon the twist angle and the characteristics of the conductive network. By doping or adding materials, such as gold, silver or NiCr, electrical conductivity of CNTs can by varied. In [5], highly conductive carbon nanotube-graphene hybrid yarns are reported. They are obtained by drawing vertically aligned multi-walled carbon nanotubes (MWCNT) into long MWCNT sheets. Then graphene flakes are deposited onto the MWCNT sheet to form a composite hybrid structure that is transformed into yarns by twisting. The electrical conductivity of these composite MWCNT-graphene hybrid yarns is over 900 S/cm. In this work, we have modeled this hybrid material as a potential data transmission line and compared it with a transmission line made out of copper on the same substrate. The results are tabulated in Table-I. They show a good agreement between copper based and composite MWCNT-graphene hybrid material based transmission lines. The hybrid material is high conductive, flexible and stretchable. This makes it suitable to use as transmission lines and connecting wires in systems that require stretching and flexibility, such as wearable systems.

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 (14mm) makes them suitable for on-body communication in healthcare applications.

A simple thin antenna with an enhanced gain for MB-OFDM UWB systems

A simple low-profile antenna with an enhanced gain is proposed for multiband orthogonal frequency-division multiplex (MB-OFDM) ultra wide band (UWB) systems. Using proximity coupling along the surface we demonstrate a technique to enhance the gain at lower UWB frequencies. The antenna is realized as a conventional CPW-fed printed disc monopole with unconventional metallic patches on the top of the substrate. With these metallic patches the antenna gain is improved especially at lower frequencies in the FCC UWB band, making it more suitable for MB-OFDM systems. Theoretical input reflection coefficient, antenna gain and radiation patterns are presented along with a complete parametric study of the proposed antenna.

Design of circularly polarised broad band stacked rectangular patch antennas for modern communication systems

Microstrip antennas are highly suitable structures for modern communication systems due to their inherent properties like low cost, small size, light weight, easy integration with host surface [1–2]. However their narrow bandwidth and low gain becomes main constraint in their practical applications. In recent times, extensive work for the improvement of bandwidth and gain has been reported [3–4]. The circularly polarized patch antennas are found useful in different communication systems and several circularly polarized patch geometries with improved performance may be seen in available literature on antennas [5–6]. In this communication, a novel antenna design is proposed to achieve circular polarization with much improved impedance bandwidth.