Desired Sidelobe Level Research Articles

AN ARBITRARY CONFORMAL ARRAY PATTERN SYNTHESIS METHOD THAT INCLUDE MUTUAL COUPLING AND PLATFORM EFFECTS

The research in the paper puts forward a novel method for synthesizing conformal arrays and optimizing low cross-polarizations including the efiects of elements mutual coupling and mounted platform. Starting from the far-fleld superposition principle, an e-cient approach with active element pattern technique is proposed to calculate the far-fleld patterns. A coordinate transform is used to create polarization quantities, and a general process for the element polarized pattern transformation is proposed. The two numerical examples are proposed, and the desired sidelobe levels and low cross- polarizations are optimized. Numerical results indicate the proposed method is valid.

Dolph–Chebyshev Beampattern Design for Spherical Arrays

Spherical arrays with array processing based on spherical harmonics have been recently studied for a wide range of applications that require three-dimensional beamforming. In this correspondence, a Dolph-Chebychev beampattern design, widely used in array processing due to the direct control over main-lobe width and maximum sidelobe level, is developed for spherical arrays within the spherical harmonics framework. We show that due to the similarity between the Legendre polynomials that define the spherical array beampattern and the Chebyshev polynomials that define the desired Dolph-Chebyshev beampattern, spherical array weights can be computed directly and accurately given desired main-lobe width or sidelobe level.

Convex objective function-based design method developed for minimizing side lobe

The existence of multiple local solutions makes it very difficult to search for filter parameters to achieve a desired side lobe level during the design of superresolution pupil filters. To deal with the difficult issue of side lobe control in the designing process, a convex objective function-based design method is developed through phase rotation and variable replacement to transform the complicated solving process with multiextreme subintervals into a simple optimization process with a convex interval. A group of constant annular complex superresolving filters are designed using the developed method. The comparison of the superresolving filters designed in this way with the well-known continuous phase filter and 3-zone multiphase diffractive superresolution filters proves the validity of the developed method.

DUAL BEAM SYNTHESIS USING ELEMENT POSITION PERTURBATIONS AND THE G3-GA ALGORITHM

The position perturbations of linear antenna elements are used for designing non-uniformly spaced reconfigurable antennas radiating with multiple pattern such that the same amplitude distribution and perturbed positions produces either a pencil or a flat topped beam, the difference being dependent upon phase distribution of the array. The perturbation method consists of inducing small perturbations in the element positions of a linear array to obtain the desired patterns and offer the flexibility of simple design and is similar to other adaptive techniques like phase only or phase/amplitude synthesis. The problem of finding the element position perturbations is treated as a non linear problem and has been solved using a the generalized generation gap steady state genetic algorithm (G3- GA) using parent centric crossover. In the G3-GA approach the population diversity versus selection pressure problem considers both the parent selection and the replacement plans of GA. The position- phase synthesis method using the G3-GA approach is compared with the G3-GA phase-only synthesis technique. It is seen that, an optimal set of element-perturbed positions in a constrained position range with uniform amplitude, unequally spaced elements with unequal phases has the potential to overcome the design challenge of phase only syntheses that uses a larger number of elements to get the same desired side lobe level. Further when the main beam is scanned it is found that the proposed method can maintain a sidelobe level .without distortion during beam steering for the angular positions studied.

An Array Beampattern Synthesis Using Partial Constrained Adaptive Optimization

One of the prominent studies conducted on the beamforming method is the Zhou and Ingram weighting function method. This method adaptively adjusts the weights of an array to meet the desired mainlobe beamwidth and sidelobe level. However, with the Zhou and Ingram method, it took up a considerably long computation time to adjust the desired sidelobe level. Therefore, in this paper, we propose a new algorithm using partially constrained adaptation which allows us to circumvent this problem and easily meet the design specification.

An Approach for Dolph-chebyshev Uniform Concentric Circular Arrays

In this paper, a new design approach for sidelobe reduction in the uniform concentric circular arrays (UCCA) is proposed. This technique is based on tapering the current amplitudes of the rings in the array by the coefficients of an even predesigned Dolph-Chebyshev linear one-dimensional array which has a number of elements that equals twice the number of rings and a prewarped sidelobe level obtained from prewarping curves. These curves map the UCCA desired sidelobe level to a level used in the design of the corresponding one-dimensional array. The UCCA with this tapering scheme is analyzed to have the lowest possible sidelobe level that may reach 53 dB below the mainlobe and the tapering weights are found to be function of the number of elements of the innermost ring and the number of rings in the array.

The relationship between mutual coefficient errors and the amplitude and phase errors of channels

In general, an accurate mutual coupling correlation is necessary for an array antenna to reach ideal sideiobe level. If the mutual coefficient matrix of an array antenna is perfectly known, one can completely compensate the effect of mutual coupling and realize the desired sidelobe level in theory. However, the mutual coefficient matrix obtained wherever by calculation on by measurement has a limited precision. In this paper, the requirements on the precision of matrix coefficient for compensation in low sidelobe array antenna are discussed. The relationship between mutual coefficient errors and the amplitude and phase errors of channels is derived.

Design of withdrawal-weighted SAW filters.

This paper presents a new design algorithm for a withdrawal-weighted surface acoustic wave (SAW) transversal filter. The proposed algorithm is based on the effective transmission loss theory and a delta function model of a SAW transversal filter. The design process consists of three steps, which eventually determine eight geometrical design parameters for the filter in order to satisfy given performance specifications. First, the number of fingers in the input and output interdigital transducers (IDTs), plus their geometrical sizes is determined using the insertion loss specification. Second, the number and positions of the polarity reverses in the output IDT are determined using the bandwidth and ripple specifications. Third, the number and position for withdrawing and switching specific fingers in the output IDT and attached electrode area are determined to achieve the desired sidelobe level. The efficiency of the technique is illustrated using a sample design of an IF filter consisting of a uniform input IDT and withdrawal-weighted output IDT. The proposed algorithm is distinct from conventional techniques in that it can optimize the structural geometry of a withdrawal-weighted SAW filter in a direct manner by considering all the performance specifications simultaneously.

Pattern synthesis for arbitrary arrays using an adaptive array method

This paper presents a new pattern synthesis algorithm for arbitrary arrays based on adaptive array theory. With this algorithm, the designer can efficiently control both mainlobe shaping and sidelobe levels. The element weights optimize a weighted L/sub 2/ norm between desired and achieved patterns. The values of the weighting function in the L/sub 2/ norm, interpreted as imaginary jammers as in Olen and Compton's (1990) method, are iterated to minimize exceedance of the desired sidelobe levels and minimize the absolute difference between desired and achieved mainlobe patterns. The sidelobe control can be achieved by iteration only on sidelobe peaks. In comparison to Olen and Compton's method, the new algorithm provides a great improvement in mainlobe shaping control. Example simulations, including both nonuniform linear and planar arrays, are shown to illustrate the effectiveness of this algorithm.

The orthogonal method for the geometry synthesis of a linear antenna array

The orthogonal method for geometry synthesis of a linear antenna array is presented. We start from an initial array, and we perturb the element positions by using an iterative procedure and applying the orthogonal method. Applications for arrays with uniform excitation give patterns with the desired sidelobe level.

Broadband beamforming for a microphone array

An array of sensors can be used in conjunction with a beamformer, which processes the sensor signals, to achieve a directional response. The beamformer has to be designed such that a beam pattern with certain desired characteristics like specific main beam direction, defined main beam shape, and desired sidelobe level is formed. Conventional methods for the design of beamformers assume sensors with ideal features and do not take the disturbance of the sound field, caused by the mounting of the array, into account. Therefore the predicted theoretical polar response and the measured response often differ significantly. This paper presents a method for optimizing a beamformer for a one-dimensional microphone array, taking into consideration nonideal features of the sensors and the mounting. Thus the actual polar response can be improved. By evaluating cross-correlation functions of the sensor signals during a calibration procedure in an anechoic chamber and minimizing the mean squared error between the beamformer output and a prescribed response, optimum parameters for the beamformer are assigned.

Low-sidelobe reflector synthesis and design using resistive surfaces

A procedure is presented for determining the resistivity of a paraboloid's reflecting surface to obtain a desired sidelobe level. The only requirement is that the normalized aperture distribution due to the feed be greater than the corresponding normalized low sidelobe distribution at every point on the reflector (i.e. the reflection coefficient of the surface >

Constrained optimization of the performance indices of arbitrary array antennas

The solution to the optimization of performance indices of array antennas such as directive gain, efficiency index, and signal-to-noise ratio, do not provide information regarding the sidelobe region of the radiation pattern. It is shown that, with proper constraints on the sidelobes, a given performance index can be optimized to give a radiation pattern with desired sidelobe levels. As most of the performance indices of an array antenna can be expressed as a ratio of two Hermitian quadratic forms, an eigenvalue method is used for the constrained optimization. This method gives explicit expressions for the excitation vector and constrained values of the performance indices. An iterative technique is used to ensure that the specified field values occur at the sidelobe peak positions. The element excitations obtained by this technique for maximum gain and uniform sidelobe level are similar to these obtained by the Dolph-Chebyshev technique.

Thinning and broadbanding antenna arrays by unequal spacings

This paper presents a theory for, and a method of designing a thinned or broad-band antenna array by means of unequal spacings. Using the theory of unequally spaced arrays developed by one of the authors, an antenna array can be designed to produce a desired beamwidth and sidelobe level with the average spacing many wavelengths apart. The patterns are expressed in a series of the Anger functions and its sidelobe level is shown to decrease approximately as <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N^{-0.5}\simN^{-0.4}</tex> where <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> is the total number of elements, and the gain is approximately equal to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> . It is also shown that the sidelobe level can be improved by varying the amplitude distribution. Numerical examples are given to illustrate the method.

A mathematical theory of antenna arrays with randomly spaced elements

Various probabilistic properties of a large antenna array with randomly spaced elements have been studied. It is found that for almost all cases of practical interest the required number of elements is closely related to the desired sidelobe level and is almost independent of the aperture dimension, the resolution (or the beamwidth) depends mainly on the aperture dimension, and the directive gain is proportional to the number of elements used if the average spacing is large. As a consequence the number of elements required is considerably less than that with uniform spacings. Starting with a given number of elements and a given aperture size, it is possible to improve the resolution by a factor of ten, a hundred, or more by spreading these elements over a larger aperture with little risk in obtaining a much higher sidelobe level and a lower directive gain. In fact, this method offers a solution which is optimum in a certain statistical sense, i.e., all sidelobes are of equal level with equal probability. In addition, this analysis also gives a simple estimate of the sidelobe level of most nonuniformly spaced antenna arrays. In a number of such arrays studied by various investigators with high speed computers, the agreement found is remarkable.