Browsing by Author "Takamizawa, Koichiro"

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    Analysis of Highly Coupled Wideband Antenna Arrays Using Scattering Parameter Network Models
    Takamizawa, Koichiro (Virginia Tech, 2002-12-10)
    Wideband phased arrays require very tight element spacing to permit wide angle scanning of the main beam over the wide bandwidth. The consequence of tight spacing is very high mutual coupling among the elements in the array. Previous efforts by Virginia Tech Antenna Group has shown that the strong coupling can be utilized in arrays to obtain broadband frequency response while maintaining a small element spacing. However, mutual coupling between elements in a tightly coupled array can sometimes dramatically change the operating frequency, bandwidth, and radiation pattern from that of the single isolated element. Thus, there are some fundamental questions that remain regarding the effective operation of highly coupled arrays for beam forming, beam scanning, and aperture reconfiguration. Existing antenna pattern analysis techniques including the active element pattern method are inadequate for the application in highly coupled arrays. This dissertation focuses on the development of a new antenna array analysis technique. The presented method is based on the scattering parameter network descriptions of the array elements, associated feed network and the active element patterns. The developed model is general. It can be applied to an array of any size and configuration. The model can be utilized to determine directivity, gain and realized gain of arrays as well as their radiation efficiency and impedance mismatch. Using the network model, the relationship between radiation pattern characteristics and the input impedance characteristics of the array antennas becomes clear. Three types of source impedance matching conditions for array antennas are investigated using the model. A numerically simulated array of strip dipole array is used to investigate the effects of various impedance matching methods on the radiation pattern and impedance bandwidth. An application of network analysis is presented on an experimental investigation of $3\times 3$ Foursquare array test bed to further verify the concepts.
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    Array antenna synthesis including element and feed coupling
    Takamizawa, Koichiro (Virginia Polytechnic Institute and State University, 1988)
    Precise radiation pattern control for an array antenna requires precise control of array element excitations. One application is that of low side lobe patterns. Classical synthesis methods for the desired pattern may not be realized in practice due to coupling effects. Coupling occurs in two forms: the mutual coupling between array elements and the coupling introduced by the feed networks. Ideally one could account for such coupling within the array architecture during the design process and alter the feed network parameters to adjust for such coupling. Unfortunately, this is a nonlinear problem requiring special solution techniques. This report presents the solution techniques for determining feed network parameter values that compensate for antenna-feed network coupling. Scattering parameter representations of the antenna array and the feed networks are used. Examples of various array configurations for microstrip antenna arrays and for dipole arrays are included.