May 2015
Intermediate
224 pages
6h 22m
English
Content preview from Timed Arrays
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4ELEMENTS IN TIMED ARRAYS
Chapters 1–3 only dealt with arrays of point sources. Point sources are not real antennas and represent a single point from which an antenna appears to radiate. The resulting array factor depends only on the point source spacing, the element weights, and the frequency. A good approximation of an array pattern is the product of the element pattern of a real antenna times the array factor. Elements determine the array bandwidth and polarization and impact the array gain. Spacing between elements limits the size of the elements that fit into the array lattice. The unit cell is the maximum area allotted to an element in the array aperture and is defined by the area dxdy. The characteristics of an isolated element (impedance, gain, polarization, etc.) change when the element is surrounded by other elements in the array. This chapter introduces potential elements for a timed array and their characteristics.
4.1 ELEMENT CHARACTERISTICS
An array of point sources is a simple model for estimating the array beamwidth, directivity, sidelobe level, and grating lobe formation. Other array characteristics depend on the type of element in the array. The array pattern approximately equals the product of the array factor and the element pattern that combines the characteristics of both the element positions and weightings with the characteristics of the element.
4.1.1 Polarization
An antenna’s polarization is defined by the polarization of a wave transmitted by ...
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