Directivity Pattern of Line Arrays
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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 whiteKeywords:
Directivity
Line (geometry)
Collinear antenna array
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This communication shows that, given the correct terminal voltages on each element, a log-periodic dipole array (LPDA) can achieve an omnidirectional radiation pattern over a wide frequency bandwidth. This cannot be achieved by analytical means, but through a global search optimization strategy. An optimization method, which achieves omnidirectional radiation of the array with maximum gain deviations of less than 0.06 dB over more than 30% bandwidth, is discussed and the results are presented.
Collinear antenna array
Wideband
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In this work we empirically show that the Emfit film can be stuck on a curved surface without influencing its original electromechanical performance. This characteristic along with the previously reported piston-like response of the film at frequencies below 150 kHz, opens up the possibility to fabricate ultrasonic transducers of complex developable substrate and subsequently, customizable acoustic field. As a first step to complex acoustic directivity patterns, a quasi-spherical substrate is proposed in order to customize an omnidirectional radiation field. Numerical simulations were used in order to show that such an omnidirectional radiation directivity pattern can be approximated by an Emfit based transducer stuck on a quasi-spherical substrate. This works shows preliminary efforts directing to build an omnidirectional, spherical ultrasonic transducer, based on Emfit film.
Directivity
Piston (optics)
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The article presents a simple, approximate formula for the directivity of an omnidirectional antenna without minor lobes. This problem has been treated before by Monser (1954), and the results have been cited by Levine and Monser (1961). In this earlier work, an approximate formula, showing antenna directivity as a function of the half-power beamwidth (HPBW), was determined by fitting a curve to data that had been obtained previously by numerically integrating across the half-power beamwidth spectrum: a process involving many integrations. Notwithstanding the evident good agreement between the "exact" and "curve-fitted" data in that instance, it is equally possible to return to the supporting sums and determine directly a very simple, alternative approximation to the defining integral and, hence, to the directivity of such antennas.
Beamwidth
Directivity
Antenna gain
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A new structure of horizontally polarized (HP) antenna array is presented for azimuthal omnidirectional coverage. The proposed antenna array is engineered by breaking the fringing held symmetry along the typical parallel strip-lines, which is implemented by loading held-block structures alternatively and periodically. In physics, the blocking structures constrain the fringing helds inside, producing a series of rectangular open cavities operating at the TM 1n0 (n = 0.5) mode. Counterintuitively, these asymmetric open cavities are able to generate an omnidirectional radiation pattern in the E plane with horizontal polarization, similar to the linear magnetic current array. In order to verify the design strategy, a hve-unit center-fed cascaded cavity array is fabricated and tested. The measured bandwidth is 120 MHz (5.83-5.95 GHz) with reflection coefhcient lower than -10 dB. The HP omnidirectional pattern at 5.9 GHz provides a gain variation of 1.94 dB ranging from 6.7-8.64 dBi.
Collinear antenna array
Ranging
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In this paper, a low-cost planar dipole array antenna with an omnidirectional radiation characteristic is presented. The proposed omnidirectional planar dipole array antenna comprises two 1/spl times/2 dipole arrays arranged back to back, and can be easily constructed by printing on both sides of a dielectric substrate. By selecting the central ground plane to have a small width (about 6 mm for operating at about 2.4 GHz), the proposed array antenna can have a good omnidirectional radiation pattern in the azimuthal plane (gain variations less than 2 dBi). Prototypes of the proposed antenna for WLAN operation in the 2.4 GHz band (2400-2484 MHz) were constructed and studied.
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An omnidirectional antenna is presented. It is composed of dipole array. This antenna operates at 2.4 GHz for WLAN. As the radiation element, the dipole has a minimized height for reducing the size of antenna. Its size is 27mm high and 75mm length. Four dipoles that encircle a metal cylinder at the radial direction form an omnidirectional element. Along the axial direction there are three omnidirectional elements with the distance of 101mm. The gain of this antenna is 7.1 dBi at 2.4 GHz and the gain variation in azimuth plane less than 0.5dB.
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In this paper, we describe 2 kinds of printed dipole arrays and compare the performances of these arrays in term of reflexion coefficient, radiation pattern and dimensions. It is interesting to design array in order to obtain better performances in term of omnidirectional radiation pattern in comparison with single element. We choose this elementary source in order to obtain compact array with good performances. These antenna arrays are designed to have omnidirectional radiation pattern with horizontal polarization. We present an application dedicated to compact base station in the last section.
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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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The paper presents a unique omnidirectional three-element dipole array that can be adjusted to provide vertical, horizontal, or circular polarization for a variety of wireless applications. The 2:1 voltage standing wave ratio bandwidth of the antenna over all configurations is greater than 10%, but performance data is presented for the personal communication services (PCS) band (1850-1990 MHz).
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Axial ratio
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The design of a two-element quasi-Yagi antenna array with omnidirectional coverage is presented. The prototype array has a 50% bandwidth (|S11| les -10 dB) of 1.2-2.0 GHz. E-plane and H-plane radiation patterns of the single antenna element are shown at 1.3 and 1.7 GHz. The prototype two-element array exhibits an omnidirectional radiation pattern in the H-plane, with a maximum gain of 4.5 dBi at 1.3 GHz with ripples of less than 2.6 dB and 2.6 dBi at 1.7 GHz with ripples of less than 1.5 dB. The antenna has potential use in broadband mobile applications.
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