Optimization of optical waveguide antennas for directive emission of light
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Optical traveling wave antennas offer unique opportunities to control and selectively guide light into a specific direction, which renders them excellent candidates for optical communication and sensing. These applications require state-of-the-art engineering to reach optimized functionalities such as high directivity and radiation efficiency, low sidelobe levels, broadband and tunable capabilities, and compact design. In this work, we report on the numerical optimization of the directivity of optical traveling wave antennas made from low-loss dielectric materials using full-wave numerical simulations in conjunction with the particle swarm optimization algorithm. The antennas are composed of a reflector and a director deposited on a glass substrate, and an emitter placed in the feed gap between them serves as an internal source of excitation. In particular, we analyze antennas with rectangular- and horn-shaped directors made of either hafnium dioxide or silicon. The optimized antennas produce highly directional emissions due to the presence of two dominant guided TE modes in the director in addition to leaky modes. These guided modes dominate the far-field emission pattern and govern the direction of the main lobe emission, which predominately originates from the end facet of the director. Our work also provides a comprehensive analysis of the modes, radiation patterns, parametric influences, and bandwidths of the antennas, which highlights their robust nature.Keywords:
Directivity
Reflector (photography)
Many authors suggest directional antennas to enhance the transmission performance of ZigBee networks. For line-of-sight propagation, directional antennas can extend the transmission range or reduce the transmit power. Directional antennas may also reduce interference between networks operating in the same frequency channel. However, these antennas may not perform similarly under non-line-of-sight propagation conditions. This work presents a study with ZigBee modules comparing the performance of a directional antenna with an omnidirectional one. The measurements were conducted on a university campus for different propagation outdoor environments. A deconvolution technique was applied to estimate the received signal as a function of the azimuth angle. The results demonstrated that the received power followed the gain difference between antennas only for paths with low attenuation. Considering the same Effective Isotropic Radiated Power (EIRP), the system with directional antennas started to lose packets at the same distance as the omnidirectional antennas. The directional antenna did not allow the increase in the link range compared to the omnidirectional antenna. The power consumption was also measured for different transmit power levels of the ZigBee radio. The study showed that the control circuits of directional antennas typically consume more power than omnidirectional antennas operating at a higher transmit power level.
Effective radiated power
Conformal antenna
Non-line-of-sight propagation
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Smart antennas are a specific type of directional antenna able to dynamically control the gain as a function of direction. This contrasts with more traditional directional antennas, where the dynamic ability is missing, and with omnidirectional antennas, which are designed to have equal gain in all directions.
Reconfigurable antenna
Conformal antenna
Reflective array antenna
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High-gain antenna
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The use of narrow beam directional antennas in wireless messaging has the potential of improving the transmission quality, increasing base station capacity, and reducing the number of base stations needed to provide a service for portable radio users. Directional antenna beams increase the protection to cochannel interference. The performance of a three-sector, twelve beam antenna system is compared with an omnidirectional and a conventional three-sector antenna configuration via computer simulation.
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Connectivity is a crucial issue in wireless networks. Gupta and Kumar show that with omnidirectional antennas, the critical transmission range for a wireless network to achieve asymptotic connectivity is O(radiclog n/n) if n nodes are uniformly and independently distributed in a disk of unit area. In this paper, we investigate the connectivity problem when directional antennas are used. We find that there also exists a critical transmission range, which corresponds to a critical transmission power. We show that in the same propagation environment, when directional antennas use the optimal antenna pattern, the critical transmission power could be much smaller than that in networks using omnidirectional antennas. Moreover, to achieve asymptotic connectivity, it is known that each node has to have O(log n) neighbors when using omnidirectional antennas. We show that even using the transmission power level at which each node has only O(1) neighbors when using omnidirectional antennas, we can still achieve the asymptotic connectivity with directional antennas.
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A 60-GHz radio is an attractive technology in wireless home networks because it can provide high data rate up to a few gigabits per second. A 60-GHz network generally uses directional antennas and has a problem of neighbor discovery (ND), although it has an advantage of high data transmissions. In particular, if a directional antenna is used in self-organized wireless ad hoc networks, the ND time and energy consumption can be significantly increased. To solve this problem, we propose a multiband directional ND (MDND) scheme, in which management procedures are carried out by using the 2.4-GHz band with the omnidirectional antennas, whereas data transmissions are performed by using the 60-GHz band with directional antennas. Analytical models on the ND time and energy consumption are also derived by considering assisted and beamforming periods in the ND procedure through the omnidirectional and directional antennas. Performance evaluation results demonstrate that the proposed scheme outperforms comparative schemes that use only directional beamforming in terms of the average ND time and energy consumption.
Neighbor Discovery Protocol
Gigabit
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One of the key element in performance measurement for a neighbor discovery algorithm with switched beam antennas is how long it takes to discover the neighbors given that nodes do not have any prior knowledge about their neighbors. An impression we may have in neighbor discovery is that algorithms based on directional antennas takes longer time for a node to discover all its neighbors than those entirely based on omnidirectional antennas. We propose two neighbor discovery schemes, one is based on time slotting and the other on the well known CSMA/CA unslotted version. We evaluate the time that the sink needs to discover its neighbors when it is equipped with a switched beam antenna, and when it uses an omnidirectional antenna. Through our simulation results, we show that when neighbor discovery algorithms based on directional antennas are correctly designed, they achieve the same order of performance in terms of time needed by the sink to discover all its neighbors as those based on omnidirectional antennas. Our simulation results also show that when using a switched beam antenna and CSMA/CA algorithm for medium access at the sink, the discovery delay is higher.
Neighbor Discovery Protocol
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This paper presents first results of experiments in vehicular-to-roadside communication using directional antennas. With directional antennas on one side, the duration of connection to a fixed access point or a road side communication unit can be extended and on the other side the interference caused to others can be reduced. In this work results of experiments with electronical steerable directional antennas mounted on a car communicating with stationary access points are presented. The measurements show the benefit of using directional antennas in different environments typical for vehicular communications. The duration of potential 802.11b connections have been compared using directional and omnidirectional antenna patterns when driving through suburban environment. This comparison is based on passive scanning for access points in order to validate the approach in realistic scenarios. The results clearly prove a substantial potential improvement when using directional antennas.
Conformal antenna
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For ultrasonic transducers employed in deep seas, omnidirectivity is often required. In this paper, an omnidirectional transducer for use in deep seas is designed. To realize a transducer with desired directivity under high hydro-pressure, a new type of construction utilizes a high-sound-speed material called syntactic foam attached to a cylindrical transducer element. Numerically designed results for the omnidirectional transducer using finite element analysis considering an infinite space agree well with measured directivity patterns, and the design of a transducer with desired directivity for use under high hydro-pressure in deep seas is found to be possible.
Directivity
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Highly directional acoustic and electromagnetic antennae are often built from linear arrays of omnidirectional transmitting or receiving elements This Demonstration plots the directivity pattern of an unshaded line array of omnidirectional elements steered to the angle with respect to the array axis The patterns have cylindrical symmetry about the array axis The array elements are plotted as white
Directivity
Line (geometry)
Collinear antenna array
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Using directional antennas in wireless networks has become a popular approach due to its benefits. However, since the existing MAC protocols were not designed to work with such antennas, when the existing protocols are used, the network capacity may even deteriorate rather than improve. In this paper, a neighbor discovery algorithm has been proposed for a system using directional antennas. A discovery algorithm proposed by [1] has been studied and its efficiency has been improved by making some changes. With directional antennas finding the neighbor can be a knotty problem, since when and where to point the beam is really critical for communication. Some proposed systems use GPS, omnidirectional antennas or time synchronization to solve these problems. However, the proposed system in this paper needs neither GPS nor omnidirectional antennas. It does not depend on time synchronization either.
Neighbor Discovery Protocol
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