Low Sidelobe Radiation Patterns Research Articles

Differential evolution to synthesize low sidelobe thinned isophoric time‐modulated planar array with increased directivity

In this article, a novel method for synthesizing rectangular planar array through thinning and time-modulation is proposed. A new differential evolution based approach that generates a rank based population is adopted to find out the optimum element off position for thinning and ontime duration to modulate the antenna elements in time domain. The proposed synthesis method defines a preservative boundary at the array center where the antenna elements are not thinned and time-modulated rather uniformly excited. It is shown that this proposed thinning and time-modulation strategy with an optimum preservative boundary helps to realize low side lobe radiation pattern with increased directivity by controlling less number of optimization variables as compared to traditional approach. It also reduces the feed network complexity specifically for large antenna arrays.

Evolutionary algorithms based synthesis of low sidelobe hexagonal arrays

Abstract In this work a procedure namely Findpeaks2 is proposed to detect the maximum sidelobe level (SLL) from the samples of three dimensional radiation pattern. This procedure detects all sidelobe peaks form the samples of the radiation pattern in the entire visible region. For illustration, a low sidelobe radiation pattern synthesis problem is formulated for two concentric regular hexagonal antenna array (CRHAA) geometries, having 6- and 8- rings. To verify the extent of applicability of the proposed procedure, both broadside and scanned array configurations are considered. Feed current amplitudes are considered as the optimizing variables. Two variations of current distributions are considered, i) identical feed for all the elements on a ring (hence the one variable per ring needs to be optimized), and ii) asymmetric excitation distribution (set of excitation amplitude of all elements as optimizing variables). The design objective has been considered to optimize the radiation patterns with very low interference from the entire sidelobe region. To restrict the fall of directivity value, a constraint on the lower limit of directivity value is considered. The impacts of symmetry and the constraint on directivity on the search of these algorithms are studied. Evolutionary algorithms like Real Coded Genetic Algorithm (RGA), Firefly Algorithm (FFA), Flower Pollination Algorithm (FPA), an adaptive variant of Particle Swarm Optimization Algorithm namely (APSO), and two recently proposed variants of DE namely Exponentially Weighted Moving Average Differential Evolution (EWMA-DE), and Differential Evolution with Individual Dependent Mechanism (IDE) are employed for this pattern optimization problem.

DESIGN OF LINEAR ANTENNA ARRAYS WITH LOW SIDE LOBES LEVEL USING SYMBIOTIC ORGANISMS SEARCH

In this paper, low sidelobe radiation pattern (i.e., pencil-beam pattern) synthesis problem is formulated for symmetric linear antenna arrays. Different array parameters (feed current amplitudes, feed current phase, and array elements positions) are considered as the optimizing variables. The newly proposed evolutionary algorithm, Symbiotic Organisms Search (SOS), is employed to solve such a pattern optimization problem. The design objective is to obtain radiation patterns with very low interference in the entire sidelobes region. In this context, SOS is used to minimize the maximum sidelobe level (SLL) and impose nulls at specific angles for isotropic linear antenna arrays by optimizing different array parameters (position, amplitude, and phase). The obtained results show the effectiveness of SOS algorithm compared to other well-known optimization methods, like Particle Swarm Optimization (PSO), Biogeography-based optimization (BBO), Genetic Algorithm (GA), Firefly Algorithm (FA), and Taguchi method. Unlike other optimization methods, SOS is free of tuning parameters; one just has to set the value of the population size and the number of iterations. Moreover, SOS is robust and is characterized by relatively fast convergence and ease of implementation.

Phase Correction Method for GO Designed Dielectric Lens Horn Antenna

In order to achieve omni-directional coverages on base station antennas for fixed wireless access systems (FWA), a TM 01 mode conical hom with 4.6A aperture size was employed as a feed hom for an axisymmetrical reflector antenna. Here, a shaped dielectric lens was inserted in the conical horn so as to achieve low sidelobe radiation characteristics. However, it was pointed out that radiation pattern shaping ability was degraded in this small lens antenna. In this paper, deteriorations of aperture distributions in a shaped lens are clarified through FDTD calculations. Severe phase delays are shown in the aperture phase distributions. A novel lens shaping method of compensating the phase delays is developed. Aperture distributions and radiation patterns of the corrected lens are estimated through FDTD calculations. Satisfactory uniform phase distributions in aperture distributions and low sidelobe radiation patterns are ensured.

A method‐of‐moments‐based algorithm to synthesize a conformal onboard array antenna

The design of low-sidelobe radiation patterns for array antennas mounted over aircrafts, ships, or any other complex platform is performed here. Both the electromagnetic coupling with the platform and the mutual coupling between the array elements are considered, and their effects are introduced in a novel synthesis algorithm. This is done by using a method-of-moments-based algorithm for three-dimensional scatters combined with an optimization procedure. The proposed method leads to a set of excitation coefficients that optimize the conformal array antenna over the vehicular platform. Some results are presented to demonstrate that high-performance radiation patterns can be synthesized. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 29: 324–328, 2001.

Design of on-board array antennas by pattern optimization

The design of low sidelobe radiation patterns for array antennas mounted over aircrafts or ships is performed by an optimization procedure. The optimization leads to a set of excitation coefficients that optimize conformal antennas over the vehicular platform considering both electromagnetic coupling with the vehicle and mutual coupling between array elements. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 21: 446–448, 1999.

Retrodirective beams and their application to low sidelobe pattern synthesis in small planar phased arrays

Beam synthesis remains one of the most difficult problems for an antenna array designer, this task being made more difficult when one limits the number of elements to a handful. Pattern synthesis in planar arrays is often achieved by the sampling of a continuous aperture distribution at the element locations. In the case of arrays of limited numbers of elements this produces errors that can unacceptably distort the radiation pattern. When one also then considers the effects of mutual coupling between the antenna elements, the application of ideal element weights derived in this way are no longer valid. In the paper a technique is presented, using the concept of retrodirective beams, that can achieve a low sidelobe beam from a continuous distribution on a circular aperture. The theory is then extended to include a planar array of antenna elements. This is achieved by the addition of retrodirective beams to the uniform beam pattern of the array. Measured data is presented for a small planar array antenna using the derived method. A method for correction of the element weights, to minimise the effects of mutual coupling, producing low sidelobe radiation patterns is then applied. No knowledge of the antenna array's coupling coefficients are required.