فهرست مطالب m. khalaj-amirhosseini

An analytic method is proposed to reduce the number of elements of a Uniformly Spaced Antenna Arrays (USAAs). To this end, both excitations and positions of a Nonuniformly Spaced Antenna Array (NSAA) are obtained by equating the Fourier's coefficients of array factors of NSAA to those of predesigned USAA, in two steps. At first step, the array is considered USAA and excitations of elements are determined. At the second step, the position of elements are determined for the excitations obtained in the first step. These two steps are repeated several times to increase the accuracy. In fact, this method is the extension of Fourier's Coefficients Equating (FCE) method previously introduced to design NSAAs. The effectiveness of the presented method for both pencil beam and shaped beam patterns is verified by some comprehensive examples.

Linear antenna arrays are synthesized to have maximum directivity for a specified beamwidth. The directivity is maximized subject to a given beamwidth such as null to null or half power one. The excitation currents are obtained using a matrix equation obtained from the Lagrange multiplier method. The performance of the proposed method is studied by means of some examples. The synthesized arrays have the pre-specified beamwhidths and their directivity is close to the number of elements.

Nonuniform Phased Sampling method is proposed to phase-only synthesize the power pattern of both linear and planar antenna arrays. This method modifies the conventional sampling method which is used for amplitude-phase synthesis. This method is based on assigning suitable phases to the sampling points of radiation pattern in order to reach desired amplitude of currents. Some examples are given to verify the effectiveness of the proposed method for both pencil-beam and shaped beam patterns.

Linear and planar antenna arrays are synthesized to have maximum directivity for a specified sidelobe level. The directivity is maximized subject to a given SLL. The beamwidth and the zeros of array factor are studied as well as the directivity. Maximum directivity-arrays are compared through some examples with super-directive, uniform, Dolph-Chebyshev and Riblet-Chebychev arrays to find a complete definition of optimum arrays. Also, the optimum value of n-bar is intuitively found for Taylor arrays.

Phase Perturbation Method (PPM) is introduced as a new phase-only synthesis method to design reflectarray antennas so as their sidelobe level is reduced. In this method, only the reflected phase of conventional unit cells are perturbed from their required values. To this end, two approaches namely the conventional Optimization method and newly introduced Phase to Amplitude Approximation (PAA) method are proposed. Finally, a reflectarray antenna is designed and fabricated to have a low sidelobe level and its performance is investigated.