Parasitic Reflector Research Articles

Parametric Analysis of Compact UWB-MIMO Antenna with Improved Isolation Using Parasitic Reflectors and Protruded Ground Strips

Parametric Analysis of Compact UWB-MIMO Antenna with Improved Isolation Using Parasitic Reflectors and Protruded Ground Strips

COMPACT TWO-PORT MIMO ANTENNA WITH HIGH ISOLATION USING PARASITIC REFLECTORS FOR UWB, X AND KU BAND APPLICATIONS

COMPACT TWO-PORT MIMO ANTENNA WITH HIGH ISOLATION USING PARASITIC REFLECTORS FOR UWB, X AND KU BAND APPLICATIONS

Dynamics of Antenna Reactive Energy Using Time-Domain IDM Method

A general computational paradigm, the time-domain infinitesimal dipole model (IDM) method, is developed and applied to compute reactive energy and radiated power for arbitrary shaped antennas with different time-domain excitations. The proposed technique first utilizes finite-difference time-domain method to compute the time-domain radiating antenna currents from near-zone electric/magnetic fields. Further, the far-zone time-domain radiated power is analytically estimated using a suitable IDM of the antenna spacetime current distributions. The time-domain reactive energy is calculated by adopting a rigorous energy subtraction approach. The proposed time-domain IDM technique is first validated by reproducing the standard antenna-Q-factor results of half-wavelength thin-wire dipoles. Second, time-domain reactive energy signatures are obtained for pulse-excited single and multiband dipole antennas, both in isolated condition and two-element multi-in multi-out (MIMO) topology. Third, the effects of parasitic reflector and director elements on the spatio-temporal energy dynamics of thin-wire Yagi-Uda antennas are demonstrated. The proposed algorithm is very general, applicable to arbitrary antenna shape and spacetime excitations, and hence is expected to enable engineers to look beyond traditional single frequency Q-factors of electrically small antennas to probe into the more fundamental spatio-temporal energy dynamics of general radiating structures, especially future generation 5G MIMO antennas.

Multiple Beam Parasitic Array Radiator Antenna for 2.4 GHz WLAN Applications

A multiple beam parasitic array radiator (MBPAR) antenna is proposed in this letter. The MBPAR antenna can cover all angles in horizontal plane by generating six wide beams with angle-step of 60° in 2.4 GHz wireless local area network (WLAN) bands. The MBPAR antenna consists of six active elements, a center parasitic reflector, twelve parasitic isolation elements, and a ground structure. Six active elements located in the ground edge use a common center parasitic reflector to realize six beams. The parasitic isolation elements located on the angular bisectors are used to improve the isolation between adjacent ports. Unlike the traditional electrically steerable parasitic array radiator antenna, the MBPAR antenna can realize six beams at the same time, which remarkably increase the communication capacity. To validate the proposed design, an MBPAR antenna has been designed and prototyped at 2.45 GHz. The MBPAR antenna exhibits VSWR <2 and isolations better than −20 dB in 2.4G-WLAN bands. The peak realized gain of 7.3 dBi and efficiency of 95.7% of the MBPAR antenna are obtained. The MBPAR antenna with large communication capacity and low wind resistance is suitable for the outdoor WLAN applications.

RF Infrastructure Cooperative System for in Lane Vehicle Localization

This paper presents a sensor which can be included in an Advanced Driver Assistance System (ADAS) that is compliant with the Vehicle to Infrastructure communication standard (V2I). This system allows estimation of the vehicle lateral position in real time by ensuring cooperation between an on-board vehicle system and passive transponders integrated in the lateral white strips of the road. Based on an optimization method, the lateral position vehicle is provided with a distance error less than 3 cm. In this paper, experimental results are presented in order to evaluate the robustness of the proposed system in a realistic environment. Three scenarios are considered to take into account the bitumen properties, the presence of parasitic reflectors in different positions around the system and the interaction between transponders.

Design of a dual‐polarised wideband short backfire antenna with high gain

The short backfire antenna (SBA) has been widely used for mobile satellite communications, tracking, telemetry and wireless local-area network applications. A dual-polarised wideband SBA excited by a hybrid configuration of waveguide and ortho-mode transducer is described here. The bandwidth widening of the antenna is achieved by the appearance of the second resonance point, owing to the parasitic reflector suspended on the conical sub-reflector. The aperture radiation efficiency is improved according to the reshaping of primary and sub-reflector, as well as the choke device added to the primary reflector. The antenna is designed to operate within the L-band. It has a frequency bandwidth for voltage standing wave ratio ≤ 1.5 of about 8% and a maximum gain of 20 dB. Within the antenna bandwidth, the gain and the radiation efficiency have values more than 19.5 dB and 76%, respectively. The designed antenna has a simple and compact construction and high mechanical and electrical characteristics; hence, it is appropriate for the satellite communication application. The operating mechanism is investigated to explain why the SBA can obtain good impedance and radiation characteristics. A parametric study is conducted for the use of practical engineering design.

Nanoimprinted diffraction gratings for crystalline silicon solar cells: implementation, characterization and simulation

Light trapping is becoming of increasing importance in crystalline silicon solar cells as thinner wafers are used to reduce costs. In this work, we report on light trapping by rear-side diffraction gratings produced by nano-imprint lithography using interference lithography as the mastering technology. Gratings fabricated on crystalline silicon wafers are shown to provide significant absorption enhancements. Through a combination of optical measurement and simulation, it is shown that the crossed grating provides better absorption enhancement than the linear grating, and that the parasitic reflector absorption is reduced by planarizing the rear reflector, leading to an increase in the useful absorption in the silicon. Finally, electro-optical simulations are performed of solar cells employing the fabricated grating structures to estimate efficiency enhancement potential.

Dual‐band reconfigurable antenna for wireless communications

AbstractA novel planar‐reconfigurable dipole antenna on ungrounded dielectric slab with parasitic reflector which has dual‐band and steerable endfire pattern characteristics, is proposed. A prototype is fabricated and both simulated and measured results validate the advantages of this antenna. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 503–505, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20016

Loop antennas for directive transmission into a material half space

The horizontal circular loop and the coaxial array of loops above a material half space are studied as antennas for directive transmission into the half space. In a practical situation the loops might be located in air with the directive transmission into the earth. In determining the optimum geometry for the single loop and the array, the far‐zone field patterns and directivities of these antennas when placed over lossless dielectrics are considered first. The directive properties for the lossless dielectric are found to be indicative of those for the same antenna over a medium with low loss when proper account is taken of the exponential attenuation experienced in the lossy medium. Parametric studies are used to obtain the maximum directivities for these antennas. For the single loop of resonant size, the optimum height over the interface is determined, and for the two‐element array consisting of a driven loop of resonant size with a single parasite, the optimum size and spacing of the parasitic reflector are found. Measured electric field patterns and gains of model antennas above an interface between air and fresh water are in good agreement with the theoretical results.

Radiation fields of open-cavity radiators and a backfire antenna

The radiation fields of an open-cavity radiator are studied theoretically and experimentally. This antenna consists of a simple open-ended circular cavity with a primary radiator, which includes a dipole, a dipole array, a terminated transmission line, and a loop, placed at an appropriate location inside the cavity. For the case of the dipole array exciter, because of the presence of a parasitic reflector in front of the dipole element, the open-cavity radiator radiates like a short backfire antenna.

A Theory of the Log-periodic Dipole Antenna†

ABSTRACT On the basis of experimentally known electrical properties, a log-periodic dipole (LPD) antenna can be divided into three regions, namely, (1) a short dipole region, (2) an active dipole region, and (3) an unexcited long dipole region. A mathematical expression for the radiation pattern of a LPD antenna is developed, assuming (a) the far field radiation pattern entirely due to the active dipole region, (b) the scaling factor T close to unity, (c) the existing mutual coupling effect to be approximately represented by the introduction of the end-fire antenna array condition, and (d) the unexcited long dipole region to function as a parasitic reflector. To simplify the analysis the proposed parasitic reflector is further assumed to be positioned just adjacent to the resonant dipole and is included in the active dipole region. Radiation patterns computed from the mathematical expression are compared with experimentally known patterns and found to be in reasonably good agreement.

A Limiting Case in the Design of an Excited Reflector Antenna

AbstractWith the increasing emphasis laid in this country at present on high power medium-wave broadcasting, preferably with directional antennae, a clear exposition of the problem of matching directional aerials was considered appropriate. The present article not merely brings together the basic theory relating to the excited reflector and the parasitic reflector, but spotlights the situation where the excited reflector breaks down. The vector diagrams help to comprehend clearly the role of the mutual impedance in altering the base impedance of the aerials to different values.

The measured performance of horizontal dipole transmitting arrays

Measurements of the performance of horizontal dipole arrays are described, and are compared with the theoretical performance under ideal conditions. The measurements include polar diagrams, the effect of ground slope and radiation through other arrays, and the performance over a frequency band of ±2% relative to the design frequency, which is typical of the width of existing short-wave broadcasting bands.One method of measurement consisted in elevating a calibrated frame receiving aerial using a captive balloon; by varying the height and position of the balloon, the field strengths in different directions from the array were measured. In the second method a frame aerial at ground level was used; this gave only relative values of field strength and was used mainly to determine the frequency characteristic.It was found that for an array radiating over a flat site free from obstacles there was good agreement between the theoretical and measured performance; the maximum field strength was of the order of 0.8–0.9 of the theoretical value. A sloping site or radiation through other near-by arrays, however, may cause appreciable departures from the theoretical characteristics.An array having no reflector curtain covers the frequency band of ±2% without appreciable loss in radiation efficiency. This is also true for an array with a parasitic reflector curtain which is tuned to the working frequency. If, however, the reflector is tuned always to the mid-band frequency, the radiation efficiency at other frequencies is reduced. The band-width can be increased by reducing the characteristic impedance of the dipoles, and measurements have been made on two types, one consisting of single wires and the other of two parallel wires spaced 6 in apart. For an array of four rows of single-wire dipoles, the band-width is ±1% for a 10% drop in field strength relative to the mid-band frequency; for a similar array of two-wire dipoles the corresponding band-width is ±2%. The band-width of arrays containing less than four rows is approximately the same.

Directional Antennas

The object of this paper is to develop analytical methods which are readily applicable to the general problems that arise in array design and to provide design curves that may be used without reference to the field theory underlying the problem. The cases of both driven and parasitic arrays have been treated. Where possible, the results have been tested by comparison with experimental results. The field and circuit conditions are treated for the case of multielement driven arrays. The effective impedance and the total radiated power, as well as the power radiated by each antenna, are determined. Expressions are given for the radiation patterns of the arrays. Examples are treated which show how these arrays are used to protect the service areas of other stations operating on the same frequency assignment. In the case of a single parasitic reflector, it is found that spacings less than a quarter wave length are desirable in both the transmitting and receiving case. It is seen that the parasitic antenna functions equally well as a director or a reflector. The case of an antenna parallel to an infinite sheet acting as a reflector is treated. It is shown that it is desirable to space the antenna very much less than a quarter wave length from the sheet. A method of measuring the mutual impedance between antennas is advanced. A systematic method of adjusting a complicated array is outlined.