DUAL FREQUENCY CIRCULARLY POLARIZED MICROSTRIP ANTENNA ARRAY
Paper contains the most valuable results of experimental and theoretical investigations of dual frequency circularly polarized microstrip antenna array for smart antenna applications with adaptive space-time processing capability. Geometry of the proposed antenna array was optimized for the operation in two frequency bands located inside IEEE L band. Presented array structure is composed from ten microstrip radiators independently excited via separate coaxial input ports. Two central radiating elements for two frequency bands have circular shapes with slits and are stacked to provide compact sizes and convergence of their phase centers. Peripheral radiators have annular ring with slits topology. Their geometric centers are superposed with the corners of virtual quadrats with the sides equal to the half of the wavelength for the appropriate band to eliminate the appearance of grating lobes and additional nulls in equivalent radiation patterns. The main feature of the array is its compact
packaging that causes significant levels of electromagnetic mutual coupling. Last influences and noticeably deteriorates the shapes of radiation patterns, purity of polarization characteristics and reflection characteristics of planar radiators. The geometric parameters of presented array were selected via multi parametric particle swarm optimization method to provide optimum performance of each radiator in compact array packaging. Moreover, several circularly polarized radiators of the described array assembly were rotated around their centers to improve their characteristics and to increase the quality and effectiveness of
latter space-time processing of adaptive antenna system. Novel design of the dual frequency circularly polarized array and imperfectness of obtained characteristics are experimentally validated.
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