Power Radiation Pattern Research Articles

Robust mask‐constrained linear array synthesis through an interval‐based particle SWARM optimisation

An innovative strategy for the robust design of linear antenna arrays is presented. Being the array elements characterised by tolerance errors, the synthesis is aimed at determining the intervals of values fitting the user-defined mask constraints on the radiated power pattern. With reference to the upper and lower bounds of the power pattern analytically determined for given tolerances through interval analysis, the nominal excitations of the array elements are then optimised by means of a global stochastic optimiser suitably customised to deal with interval numbers. A set of numerical examples is reported to show the behaviour of the proposed method as well as to assess its potentials in dealing with the robust synthesis of pencil and shaped beams.

An Octave Bandwidth Frequency Independent Dipole Antenna

Precision measurements of the spectrum of the cosmic radio background require frequency independent antennas of small electrical dimensions. We describe the design of a wide-band fat-dipole antenna with a sinusoidal profile having a frequency independent performance over the octave band 87.5 to 175 MHz. The input return loss exceeds 15 dB and the radiation power pattern is frequency invariant and close to cosine square over the octave bandwidth. The structure has been optimized using electromagnetic modeling, and the design has been validated by constructing a prototype.

Analysis of the Pattern Tolerances in Linear Arrays With Arbitrary Amplitude Errors

The analysis of the tolerances on the power pattern of an array of electromagnetic radiators having excitation amplitudes affected by random errors around the nominal values is addressed. Toward this end, an analytic strategy based on interval analysis is exploited to predict the bounds of the variations in the radiated power pattern in correspondence with difference models of the amplitude tolerances. Selected results are presented and discussed in a comparative fashion as well.

Light extraction efficiency enhancement in light-emitting diodes with indium tin oxide nano-craters

A simple and low cost method is described which improves extraction efficiency. The indium tin oxide (ITO) textured film was fabricated by using the self-assembly method and dry-etching. The surface morphologies and surface roughness were observed by using an atomic force microscope. The I−V characteristics, output power and polar radiation pattern of the LEDs with and without textured ITO were measured for comparison. Cylinders and craters were formed on the ITO surface after the etching, the height of which increased with etching time. The output power of the devices is proportional to the etching time. Total internal reflection of light on the ITO-GaN interface is reduced due to the appearance of cylinders and craters, and their increasing height. Thus, the output power is improved.

Can Radiators Be Really Isotropic?

In search for isotropic radiators with reasonable quality Factor (Q), bandwidth, and efficiency, one looks for practical radiators with a typical resonant length of . We present here a Green's function analysis in Fourier of a microstrip element and a far-field integral method in configuration (real) space of single and dual U-shaped elements. Both solutions analytically prove that the power radiation patterns are isotropic in nature (while the thickness and the width tend to zero), although the polarizations are not symmetrical in all cuts. It is also shown that the power isotropic U-shaped radiator, for which the surface current density is infinite, can be replaced by another finite-size radiator, having finite-surface current density, such that its far-field is exactly the same as the far-field of the U-shaped isotropic radiator.

Perturbation Analysis of a Planar Periodic Leaky-Wave Antenna Fed by Surface Waves

We consider a printed leaky-wave antenna composed of a grounded substrate topped by a periodic metallic screen or grating. The antenna is fed by the TMo surface-wave mode that is launched by an array of slots in the ground plane. The leaky-wave attenuation and phase constants are derived using a simple but accurate field perturbation approach. The radiation power, directivity, and beam patterns are also deduced. Numerical results show that, depending on the screen period and the substrate height, there is an optimum frequency range for maximum radiative power. In addition, calculated results are also in agreement with simulations and measurements for some recently designed and fabricated structures.

Design of an Omnidirectional Multibeam Transmitter for High-Speed Indoor Wireless Communications

For future high speed indoor wireless communication, diffuse wireless optical communications offer more robust optical links against shadowing than line-of-sight links. However, their performance may be degraded by multipath dispersion arising from surface reflections. We have developed a multipath diffusive propagation model capable of providing channel impulse responses data. It is aimed to design and simulate any multibeam transmitter under a variety of indoor environments. In this paper, a multi-beam transmitter system associated with hemisphere structure is proposed to fight against the diverse effects of multipath distortion albeit, at the cost of increased laser power and cost. Simulation results of multiple impulse responses showed that this type of multi-beam transmitter can significantly improve the performance of BER suitable for high bit rate application. We present the performance and simulation results for both line-of-sight and diffuse link configurations. We propose a design of power radiation pattern for a transmitter in achieving uniform and full coverage of power distributions for diffuse indoor optical wireless systems.

A reconfigurable plasma antenna

An experiment aimed at investigating the antenna properties of different plasma structures of a plasma column as a reconfigurable plasma antenna, is reported. A 30 cm long plasma column is excited by surface wave, which acts as a plasma antenna. By changing the operating parameters, e.g., working pressure, drive frequency, input power, radius of glass tube, length of plasma column, and argon gas, single plasma antenna (plasma column) can be transformed to multiple small antenna elements (plasma blobs). It is also reported that number, length, and separation between two antenna elements can be controlled by operating parameters. Moreover, experiments are also carried out to study current profile, potential profile, conductivity profile, phase relations, radiation power patterns, etc. of the antenna elements. The effect on directivity with the number of antenna elements is also studied. Findings of the study indicate that entire structure of antenna elements can be treated as a phased array broadside vertical plasma antenna, which produces more directive radiation pattern than the single plasma antenna as well as physical properties and directivity of such antenna can be controlled by operating parameters. The study reveals the advantages of a plasma antenna over the conventional antenna in the sense that different antennas can be formed by tuning the operating parameters.

Power ultrasonic transducers with extensive radiators for industrial processing

High-power ultrasonics (HPU) is a green emerging technology that offers a great potential for a wide range of industrial processes. Nevertheless such potential have remained restricted during many years to a limited number of applications which reached commercial development. The possible major problem for extending the range of HPU industrial applications has been the lack of power ultrasonic transducers for large-scale application, adapted to the requirements of each specific problem with high efficiency and power capacity. A new family of HPU transducers with extensive radiators have been recently introduced. It comprises a variety of transducer types designed with the radiators adapted to different specific uses in fluids and multi-phase media. Such transducers implement high power capacity, high efficiency and radiation pattern control. In addition, their design incorporate strategies to eliminate or reduce modal interactions produced at high power as a consequence of their nonlinear behaviour. The introduction of such new transducers has significantly contributed to the development at semi-industrial and industrial level of a number of processes in the food and beverage industry, in environment and in manufacturing. This paper deals with the basic structure and main characteristics of such transducers as well as their performance in the developed application processes.

An efficient mode conversion configuration in relativistic magnetron with axial diffraction output

Relativistic magnetron with diffraction output, also known as magnetron with axial extraction, is a favorite in exploring the most compact narrow band high power microwave source. For further improving power conversion efficiency and radiation pattern without diminishing the compactness, this paper proposed an efficient mode conversion configuration in an S-band π-mode operating relativistic magnetron with diffraction output. The whole device has a total length of 290mm and a maximum diameter of 260mm. In three-dimensional particle-in-cell (PIC) simulation, an optimized outcome that the power conversion efficiency can reach 43% corresponding to 4.2GW output and the radiation pattern is similar to TE11 mode is achieved.

Axially slotted antenna on a spheroid with an isorefractive coating

An algebraic solution is presented to the problem of radiation from an axisymmetric slot on a conducting prolate spheroid confocally coated with an isorefractive material, when the slot is excited by a delta gap source. The formulation of the problem is realized by expanding the electromagnetic field in each region in terms of spheroidal vector wave functions and a set of unknown expansion coefficients. Imposing the boundary conditions at the interface between the surface of the spheroid and the isorefractive coating, as well as that between the coating and the medium exterior to the coating leads to a set of simultaneous equations, the solution of which yields the unknown expansion coefficients. Numerical results are presented as normalized power patterns and radiation patterns for isorefractive materials, to show the effects of the coating on the radiation from the antenna.

Diffraction of the radiation of an electric dipole arbitrarily positioned inside a corner reflector

The method of the uniform geometric theory of diffraction (UGTD) was used to solve a 3D diffraction problem of the radiation of an electric dipole arbitrarily positioned inside a 90° reflector with finite dimensions. For three mutually orthogonal orientations of a half-wave dipole, space radiation-power patterns are calculated and the field structure is analyzed. The influence of diffraction effects at the reflector edges on the field intensity in the direction of the maximum of the dipole’s radiation field and the dipole’s radiation resistance is studied as a function of the dipole position relative to the reflector sides.

Lightwave Antenna With A Small Aperture Manufactured Using MEMS Processing Technology

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> High-performance antennas at lightwave frequency require optimal curved surfaces and high mechanical precision in order to realize high aperture efficiencies. We have developed a novel micro lightwave antenna by employing the micro electromechanical system processing technology. We describe a transparent antenna that has a multilevel step structure with a diameter of 4 millimeters. The ideal curve of the antenna surface is discretized by steps of constant height. The characteristics of the fabricated antenna have been measured; its gain is 84.1 dBi, which is 0.83 dB less than that of a reference antenna with a uniform field distribution. The aperture efficiency is 82.6%. The power radiation pattern is measured through the Fourier transform lens method and is in good agreement with the simulation result. </para>

Integration of omnidirectional wrapped microstrip antennas into laptops

The integration of a novel quasi-omnidirectional low-profile microstrip antenna element into laptop computers is proposed. The antenna structure is obtained by wrapping a patch element around the top edge of the laptop screen. The antenna is fed by a microstrip inverted line, which can be easily integrated inside the plastic display cover. Experimental results show that very good total power radiation pattern omnidirectionality and an adequate coverage of the whole 2.4-GHz ISM band are achieved. An antenna with six elements and low-mutual coupling, aiming at multiple-input-multiple-output (MIMO) arrangements, has been fabricated and tested. Experimental results confirm the fulfillment of the requirements for MIMO applications in laptops.

Feeding in-phase dipole arrays: a tutorial and a MATLAB program

Here, we revisit a textbook example of how to design a dipole array and its feed network. The effects of mutual coupling are taken into account, so that a desired set of in-phase excitations is fed to the antenna and radiated efficiently. A MATLAB M-code program, implementing the procedure and plotting the resulting radiation power pattern, is also provided.

Direction-of-arrival estimation using radiation power pattern with an ESPAR antenna

An approach for estimating direction-of-arrival (DoA) based on power output cross-correlation and antenna pattern diversity is proposed for a reactively steerable antenna. An "estimator condition" is proposed, from which the most appropriate pattern shape is derived. Computer simulations with directive beam patterns obtained from an electronically steerable parasitic array radiator antenna model are conducted to illustrate the theory and to inspect the method performance with respect to the "estimator condition". The simulation results confirm that a good estimation can be expected when suitable directive patterns are chosen. In addition, to verify performance, experiments on estimating DoA are conducted in an anechoic chamber for several angles of arrival and different scenarios of antenna adjustable reactance values. The results show that the proposed method can provide high-precision DoA estimation.

Size-reduction of pre-fractal Sierpinski monopole antenna

A method for decreasing the height of a fractal Sierpinski monopole is presented. The method is based on the construction of a wire Sierpinski monopole with a Koch island loop as initiator. This initiator changes the perimeter of the gasket while preserving the multiband behaviour and the radiation power pattern characteristics of the conventional Sierpinski gasket.

Faster than Fourier: ultra-efficient time-to-frequency-domain conversions for FDTD simulations

This tutorial compares several methods of converting from the time to the frequency domain for FDTD simulations. Applications include calculations of field or power distributions, antenna impedance, and radiation patterns. The traditional Fourier-transform methods are compared to two methods based on the solution of linear equations. This tutorial describes how to program and use these techniques, and evaluates their effectiveness for several applications, including analysis of a millimeter-resolution human model underneath a 60-Hz power line, antenna-radiation pattern and impedance calculations, the calculation of the coupling of a cellular telephone to the human head, and geophysical-prospecting simulations.

Generation of nonminimum phase from amplitude-only data

A method is presented for the generation of nonminimum phase from amplitude-only data. The nonminimum phase is generated utilizing the principles of causality and the Hilbert transform. The application of the theory has been applied to some antenna radiation-power patterns and to measured transfer functions of microwave filters to illustrate the applicability of this approach.

Radiation of an aperture antenna covered by a spherical-shell chiral radome and fed by a circular waveguide

This paper presents a full-wave analysis of the radiation characteristics of an aperture antenna that is flush-mounted on a ground plane and fed by a circular waveguide supporting the dominant TE/sub 11/ mode. The antenna is covered by a dielectric hemispherical chiral radome. Huygen's equivalence principle and the image theory are utilized to simplify the problem. The magnetic dyadic Green's function for the three-layered geometry is formulated and applied to analyze the radiated electromagnetic fields outside the chiral radome. Both the exact and approximate expressions of electric fields valid for the Fresnel and Fraunhofer zones are obtained using the spherical vector wave functions and their approximations in the far zone. Various chiral materials are assumed and computations of antenna parameters are carried out. The effects of the dielectric chiral radome on the radiation power patterns, sidelobe levels, and 3-dB beamwidths are also discussed numerically.