An efficient method based on bees algorithm (BA) for the pattern synthesis of linear antenna arrays with the prescribed nulls is presented. Nulling of the pattern is achieved by controlling only the amplitude of each array element. Numerical examples of Chebyshev pattern with the single, multiple and broad nulls imposed at the directions of interference are given to show the accuracy and flexibility of the BA.

/pdf/amplitude-only-pattern-nulling-of-linear-antenna-arrays-with-359g33ovfv.pdf

Amplitude-Only Pattern Nulling of Linear Antenna Arrays with the Use of Bees Algorithm

Null steering methods usually involve costly and complicated amplitude and/or phase control systems. A technique is presented for null steering based on the element position perturbations. The technique frees the phase shifters to be used solely for steering the main beam toward the direction of the desired signal. It also removes the limitations of the other techniques by independently steering the main beam and the nulls to arbitrary independent directions. This technique is also capable of obtaining sidelobe cancellation and wideband signal rejection. >

Null steering in phased arrays by controlling the element positions

Optimum weighting of adaptive antenna arrays is accomplished by computing the weight vector that maximizes the signal-to-interference-plus-noise ratio (SINR). The optimal weight vector is in general complex with each weight having different magnitudes and phases. However, the design of some antenna arrays facilitates phase-only weighting or phase-only adjustments, whereupon it is desirable to compute the constrained optimal weight vector whose components have fixed magnitudes but variable phases. This constrained optimization problem may be posed as the problem of maximizing the SINR on the space of phase-only vectors. This paper addresses the problem of computing optimal phase-only adaptive weight vectors by exploiting several properties of phasor and matrix algebra. Two new algorithms (the phase-only conjugate gradient and phase-only Newton's method) are introduced. The convergence properties. SINR performance, sidelobe level performance, and nulling performance of these algorithms are demonstrated using simulations and experimental data.

Optimum phase-only adaptive nulling

In this paper, circular and hexagonal array geometries for smart antenna applications are compared. Uniform circular (UCA) and hexagonal arrays (UHA) with 18 half-wave dipole elements are examined; also planar (2 concentric rings of radiators) uniform circular (PUCA) and hexagonal arrays (PUHA) are considered. The effect of rotating the outer ring of the PUCA is studied. In our analysis, the method of moments is used to compute the response of the uniform circular and hexagonal dipole arrays in a mutual coupling environment. The particle swarm optimization (PSO) algorithm is used to optimize the complex excitations, amplitudes and phases, of the adaptive arrays elements for beamforming.

/pdf/a-comparison-between-circular-and-hexagonal-array-geometries-nehreklzqq.pdf

A Comparison Between Circular and Hexagonal Array Geometries for Smart Antenna Systems Using Particle Swarm Optimization Algorithm

A useful and flexible method based on the tabu search algorithm for the pattern synthesis of linear antenna arrays with the prescribed nulls is presented. Nulling of the pattern is achieved by controlling the amplitude-only and both the amplitude and phase of each array element. To show the versatility of the present method, some design specifications such as the sidelobe level, the null depth and the dynamic range ratio are considered by introducing a set of weighting factors in the cost function constructed for the tabu search algorithm. Several illustrative examples of Chebyshev pattern with the imposed single, multiple and broad nulls are given.

/pdf/null-steering-of-linear-antenna-arrays-using-a-modified-tabu-52pmdmijnk.pdf

Null steering of linear antenna arrays using a modified tabu search algorithm

Several methods for synthesis of array antenna patterns with prescribed nulls are reviewed. Methods based on full amplitude/phase control at each array element and methods with a restricted number of degrees of freedom are compared, with attention focused on the characteristic features of the resultant patterns. These features are largely independent of any algorithm for achieving the nulls, and therefore they also provide a perspective on the performance of adaptive antenna systems, which employ these various control architectures.

R. Shore

Papers

Methods for null control and their effects on the radiation pattern