Fundamental properties and optimization of broadside radiation from uniform leaky-wave antennas

In this paper, radiation at broadside is studied for a general class of leaky-wave antennas (LWAs) comprised of a grounded slab covered with a partially reflecting surface, on the basis of a simple transverse equivalent network model of the structure. The analysis of the one-dimensional (1-D) version of such a LWA excited by a line source shows that a central role in establishing the features of broadside radiation is played by the condition that the phase and attenuation constants of the leaky mode responsible for radiation are equal. When this happens, a beam with a single peak at broadside is on the verge of splitting into two distinct peaks, and maximum power density is radiated at broadside. Design formulas to achieve such an optimized condition, as well as approximate expressions for the frequency bandwidth and pattern beamwidth of the antenna and for the leaky-wave phase and attenuation constants are derived, both in the absence and in the presence of losses; in addition, an optimal-beamwidth condition (which gives the narrowest broadside beam) is derived. Finally, all the results are extended to the practical case of a 2-D LWA excited by a horizontal dipole.     

A new quasi-Yagi antenna for planar active antenna arrays

In this paper, a novel broadband planar antenna based on the classic Yagi-Uda dipole antenna is presented, and its usefulness as an array antenna is explored. This “quasi-Yagi” antenna is realized on a high dielectric-constant substrate, and is completely compatible with microstrip circuitry and solid-state devices. This antenna achieves a measured 48% frequency bandwidth for voltage standing-wave ratio <2, better than a 12-dB front-to-back ratio, smaller than -15 dB cross polarization, and 3-5-dBi absolute gain. Mutual coupling of the antenna in an array environment is investigated. Finally, three simple arrays are presented, demonstrating the usefulness of the antenna as an array element. This novel antenna should find wide application in wireless communication systems, power combining, phased arrays, and active arrays, as well as millimeter-wave imaging arrays     

Evaluation of directivity for planar antenna arrays

In this paper, the directivity, including phase shift factors, for several types of uniformly excited planar arrays is obtained. Four types of dipole arrays are considered: arrays of collinear short dipoles, and of parallel short dipoles; and broadside and end-fire arrays of crosses of short dipoles. Curves of directivity versus inter-element spacing and scan angle for planar arrays with these element power patterns are presented     

A spectral domain approach for computing the radiation characteristics of a leaky-wave antenna for millimeter waves

A new method for evaluating the complex propagation constantbetain a leaky-wave structure comprising thin metallic rectangular strips etched on a dielectric rod of rectangular cross section is described. The radiation pattern of the leaky-wave antenna can be determined oncebetais known, since Re(beta) governs the direction of the main beam and Im(beta) accounts for the beamwidth and aperture efficiency. In addition the knowledge of the dependence ofbetaon frequency allows one to design the antenna for frequency-scanning applications. The method employed in this communication is based on the spectral domain approach that formulates the eigenvalue problem in the Fourier transform domain. Computed results are shown to be in very good agreement with experimental measurements.     

Design of different planar geometries of antenna arrays for isoflux radiation in GEO satellites

The synthesis of different planar geometries of antenna arrays for isoflux radiation is presented in this paper. This synthesis considers the reduction of the side lobe level and the isoflux radiation requirements for Geostationary Earth Orbit satellites. The behavior of the radiation is studied in three geometries of two-dimensional antenna arrays such as uniform planar arrays, aperiodic planar arrays (APA) and concentric ring arrays (CRA). The well-known methods of genetic algorithm and particle swarm optimization are utilized for the optimization problem. In this way, the designs of APA and CRA presented in this paper could provide an acceptable solution for reducing the antenna hardware and simplifying the power feeding even more than results presented previously in the literature.     

Frequency tunable monopole coupled loop antenna with broadside radiation pattern

A frequency tunable antenna made with an open-circuit monopole coupled loop antenna associated to a varactor diode is presented. The proposed antenna shows a 35.8% relative bandwidth, covering the 470?675 MHz frequency range. Theoretical and experimental results of S₁₁, radiation patterns and gain have been performed and show good agreement.     

The theory of broadside arrays

The general King-Sandler array theory has been examined in detail for the case of broadside arrays. Since it is not necessary to assume identical current distributions on every element in the array, a distinction is made between specified base currents and voltages. The driving-point impedances for specified base currents and voltages are presented for arrays of up to 25 elements. The effect of interaction between the element currents in the base impedances and radiation patterns is clearly shown for the broadside array. The results indicate that the major effect of unequal current distributions in the broadside array is to cause important variations in the driving-point impedances and little effect in the radiation patterns.     

An improved calculation procedure for the radiation pattern of acylindrical leaky-wave antenna of finite size

A method is given for calculating the radiation pattern of a finite-size cylindrical leaky-wave antenna structure consisting of a single source near a planar surface that supports leaky-wave propagation. The method accounts for the finite radius of the planar surface by subtracting the radiation from that part of the leaky wave that lies beyond the physical surface, from the exact radiation pattern corresponding to an infinite planar surface. Experimental results obtained for a leaky-wave structure consisting of multiple dielectric layers above a ground plane confirm the improved accuracy of the method, particularly for the part of the radiation pattern away from the peak     

Symmetry properties of linear broadside arrays

Optimality properties are proved for arrays that exhibit symmetry about their geometric centers. Specifically, a symmetric array has smaller sidelobes than a nonsymmetric one; this is true not only for exact realization but, in the worst case, for inexact realization as well.     

Novel analysis and design approaches of the planar antenna arrays

New approaches for the determination of the radiation characteristics of planar arrays are proposed. Conventionally, the best compromise directivity-side lobes level is achieved using Dolf-Chebyshev amplitude distribution. However, classical distribution forms present disadvantages in calculation time, possibility in analyzing larger arrays and the array factor is only optimum in the two principle planes. To overcome these problems, the excitation amplitudes are written under the modal form. The obtained radiated fields compared with measurement results validate the technique. It is also shown that square arrays provide improved performances from point of view of directivity compared to those of rectangular arrays with comparable size. However, above specific array size, the directivity saturates. For this, another modification of the array factor of Chebyshev square array is proposed. The modification preserves the radiation pattern configuration (same number of null radiation directions and sidelobes) and improves both directivity and side lobe levels. Analytical expressions of the array factor, the directivity, maximum half-power beamwidth, and the maximum spacing between elements have been derived. It has been shown that the use of this new technique results in an improved directivity with respect to the classical Chebyshev for a square arrays identical in size, element spacing, direction of the main lobe and side lobes level.     

A contoured beam synthesis technique for planar antenna arrays withquadrantal and centro-symmetry

A method is described for the synthesis of planar array antennas with prescribed contoured beams. The technique utilizes a transformation which divides the problem into two decoupled subproblems. One subproblem involves the determination of certain coefficients of the contour transformation in order to achieve the required footprint contours. The number of coefficients which need to be used depends on the complexity of the desired contour, but is very small in comparison to the number of planar array elements. The other subproblem consists of a linear array shaped beam synthesis, for which there already exist powerful methods for determining appropriate element excitations. The size required for this prototype linear array depends on the number of contour transformation coefficients used and the size of the final planar array. Simple formulas then determine the final planar array excitations from the information forthcoming from the above two subproblem solutions     

Combined antenna and linear arrays for radiation low-power picosecond pulses

A wire model and a combined antenna for radiation of low-power bipolar pulses with a duration of 200 ps, which is based on this model, are developed. The frequency-domain characteristics of the model and the time- and frequency-domain characteristics of the combined antenna are studied. Linear antenna arrays based on the developed combined antenna are designed and the radiation characteristics of these antennas in the wave-beam scanning mode are analyzed.     

A combined full-wave BCG-FFT method for radiation of microstrip antenna arrays

A method of combining BiConjugate Gradient(BCG) with Fast Fourier Trans-form(FFT) to analyze the radiation of microstrip antenna arrays is presented, where the spatially discrete BCG-FFT for analyzing microstrip structure is used and the del operators on Green's functions are transferred from the singular kernel to the expansion and testing functions. The resultant equations are solved by using BCG method in which the matrix-vector product is evaluated efficiently with FFT. The calculated patterns are in good agreement with the measured data.     

Investigation on antenna coupling in pulsed arrays

Pulsed arrays are becoming popular in new ultrawide-band applications to achieve long-range coverage, high capacity and to identify the angle of arrival of multiple echoes in complex environments. As in the monochromatic regime, distortion of ultrawide-band transmitted and received signals can result from the coupling between individual radiators that are in close proximity. This paper investigates the time-domain coupling in finite arrays that radiate short pulses, by introducing the concept of time-domain "active" array factor and "active" element factor. The proposed model highlights the signal-distortion phenomenology and obtains useful guidelines to reduce pulse coupling, even in dense arrays, by a proper choice of the geometrical and electrical parameters.     

NRD leaky-wave antenna for narrow beams in 94GHz

Theoretical analyses and numerical results of NRD leaky-wave antenna are presented. The results show that the characteristics of frequency scanning and very narrow beam can be implemented by NRD leaky-wave antenna. At the freguency of 94GHz, the half-power beamwidth of 0.14° of the antenna canbe obtained when the length of the antenna is 1.5m. From 90 to 98GHz, frequency scanning is about ±7° relating to the beam angle at 94GHz. The theoretical results are compared with the experimental data.     

Dual reflector antenna with narrow broadside beam for omnidirectional coverage

A new type of high gain omnidirectional antenna is presented, particularly suited for higher frequencies (e.g. millimetre waves): it is obtained with an axially symmetric dual reflector system, fed with an unconventional feed with conical pattern. The feed radiated field, after reflection on the parabolic subreflector and on the conical main reflector, is uniformly scattered in the plane perpendicular to the axis of the system, with vertical polarisation and narrow vertical beamwidth.<>     

TIME-DOMAIN RADIATION CHARACTERISTICS OF V-DIPOLE ARRAYS

The time-domain radiation characteristics of a three V-dipole array have been stud-ied by direct time-domain method.Some valuable results are obtained.