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By John G. Webster (Editor)

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Extra resources for 02.Antennas and Propagation

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Because the electrical properties of ferrite change depending on an applied bias magnetic field, this process yields the desired phase shift. Ferrite phase shifters are essentially low-cost, bulky, devices with high power handling capability. Switching-circuit shifters are essentially low-power pin diodes or FETs used as switching (ON–OFF states) elements. Depending on the applied bias current, these devices work either as short or open circuits. The phase shift is the result of an extra section of transmission line added to the switching element.

In fact an element in an array does not radiate the same pattern as if it were radiating in an isolated environment, nor does it present the same impedance or support the same current or field distribution. These effects are all evidence of a phenomenon called mutual coupling, depicted in Fig. 9(a), by which every element of the array interacts or couples with every other element. In the general case even the shape of the current distribution on each element changes with scan angle, and one must use a higher-order current approximation to evaluate the total radiation for each angle in space.

The panel is then inserted into the array as a brick into a wall. Figure 2(b) shows an array made up of area subarrays called tiles. Tiles tend to be multilayer geometries with the power divider network and elements occupying different layers in the same tile. The tiles are placed side by side to build the array. These fundamentally different organizations dictate (and in turn are dictated by) the selection of solid-state components, circuitry, and the array elements. In addition to such constrained networks, a number of arrays are built using space feeds, wherein a horn antenna illuminates the back or front face of an array to provide power division.

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