Search results for "Directional antenna"
showing 9 items of 19 documents
Printed Antennas for Sensor Applications: A Review
2014
With the expansion in number and requirements of modern wireless communications, the technology related to their associated antennas has been continuously improved. Among other options, printed antennas offer excellent features, such as low weight, profile, and cost, while maintaining good performance characteristics. In addition, their straightforward integration with electronics has opened new fields of application such as smart sensing systems. Printed antennas can be used in different parts of a wireless smart sensor as a radio link, sensing element, or even as energy harvester. In this paper, we present a thorough review of recent advances of printed antennas as regards their use in sm…
A space-division time-division multiple access scheme for high throughput provisioning in WLANs
2005
Directional antennas may dramatically increase the capacity of a Wireless LAN by allowing several stations to simultaneously communicate. Since deployment of directive/smart antennas on the customer's terminals is awkward (for technological, cost, robustness, and convenience reasons) it is of interest to deploy advanced antenna solutions only at the Access Point. When omnidirectional transmissions are used at the Mobile Stations, the asynchronous nature of the 802.11 MAC handshake structurally limits the possibility to exploit spatial reuse. Significant throughput enhancements can be achieved only at the expense of redesigning (part of) the 802.11 MAC protocol: mainly a form of synchronizat…
FDTD analysis of E-sectoral horn antennas for broad-band applications
1997
The finite-difference time-domain (FDTD) method is applied to study the performance of E-plane sectoral horn antennas designed for broad-band applications. These antennas (proposed for 6-18 GHz phased arrays) have a large bandwidth, and they are easily array integrated. These antennas have a highly complicated geometry that is modeled using a polygonal approximation in the curved boundaries. Perfect matched layers (PMLs) combined with first-order absorbing boundaries are employed to simulate the free-space environment in the FDTD mesh.
Minimization of a rectangular patch using genetic algorithms
2002
In recent years, the miniaturization of antennas have become more and more important, especially in connection with subscriber transceivers for cellular systems. Due to the multiple scattering environments and the almost indefinable operating scenario, the crosspolarization characteristics of the antenna are less important, however its physical size is critical. The attempts to reduce the physical size of the antenna made in the past, used classical methods, such as embedding the antenna in a dielectric medium of a high permittivity, adding a resistive element in series with the antenna, etc., but little effort was invested in simply generating other geometries, which by their intrinsic pro…
The Influence of a Magnetized Plasma Column on the Radiation Characteristics of a Strip Loop Antenna
2014
The radiation characteristics of a circular loop antenna located on the surface of an open waveguide in the form of an axially magnetized plasma column are studied using the rigorously obtained current distribution of such an antenna. The radiation resistance of the antenna excited by a time-harmonic external voltage is obtained for the case where the plasma inside the column is resonant. The distribution of the radiated power over the spatial spectrum of the excited waves is found and discussed.
Tuneable multicoloured patterns from photonic cross-communication between cholesteric liquid crystal droplets
2014
Monodisperse droplets of planar-aligned cholesteric (N*) liquid crystal exhibit an intriguing capacity for photonic cross-communication, giving rise to colourful patterns that depend sensitively on the N* pitch, droplet positions and illuminated area. The phenomenon results from a combination of omnidirectional selective reflection of N* droplets—which thus act as spherically symmetric self-assembled photonic crystals—and total internal reflection at the continuous phase surface. We outline how the unique optical properties can be employed in numerous applications.
Evaluating the user experience of omnidirectional VR walking simulators
2020
Abstract Omnidirectional treadmills (ODTs) have been traditionally proposed as a promising solution for users’ navigation in large-scale virtual environments. These mechanical devices enable users to perform locomotive motion with 360-deg freedom, while keeping their position fixed in the physical world. However, most locomotion approaches based on omnidirectional treadmills have presented either high acquisition or maintenance costs, being the capabilities of the general public, or a limited reliability. In this paper, we present a comparative usability and acceptance study with real users evaluating the two most common approaches for the development of this type of Virtual Reality (VR) wa…
Optical flow estimation from multichannel spherical image decomposition
2011
The problem of optical flow estimation is largely discussed in computer vision domain for perspective images. It was also proven that, in terms of optical flow analysis from these images, we have difficulty distinguishing between some motion fields obtained with little camera motion. The omnidirectional cameras provided images with large filed of view. These images contain global information about motion and allow to remove the ambiguity present in perspective case. Nevertheless, these images contain significant radial distortions that is necessary to take into account when treating these images to estimate the motion. In this paper, we shall describe new way to compute efficient optical fl…
A Dataset of Annotated Omnidirectional Videos for Distancing Applications
2021
Omnidirectional (or 360°) cameras are acquisition devices that, in the next few years, could have a big impact on video surveillance applications, research, and industry, as they can record a spherical view of a whole environment from every perspective. This paper presents two new contributions to the research community: the CVIP360 dataset, an annotated dataset of 360° videos for distancing applications, and a new method to estimate the distances of objects in a scene from a single 360° image. The CVIP360 dataset includes 16 videos acquired outdoors and indoors, annotated by adding information about the pedestrians in the scene (bounding boxes) and the distances to the camera of some point…