provided (as we shall show below) the movement is not too rapid. This remark applies, of course, only to pointing accuracy, not to side lobe levels or other characteristics of the antenna. Locating all the PCC’s in one small volume very near the reference element may be difficult if the array contains thousands of elements. A modification of the central phasing idea using a tree topology in which the phase reference is regenerated at each node will be required in such large arrays. This is illustrated in Figure 3. Each branch of the tree consists of a PCC, located near the node, and an element of the ARA at the end of a transmission line. A phase reference supplies all the PCC’s connected to a node. At the initial node, this is the reference element of the array. At subsequent nodes, it is a phase reference regenerator (PRR). The PRR combines samples of the pilot and conjugate signals at an element to reproduce the original reference. Specific ways of doing this will be described in the discussion of PCC’s in Subsection B below. The dashed boxes in Figure 3 contain all the circuit elements located at a node. Since the signal paths within these node assemblies are unilateral, their phase delays must be carefully balanced in order to avoid phase error buildup at successive nodes. In order to assure the stability of the phase delay balance, these assemblies must be uniform and compact. Critical applications may require temperature stabilization of some active elements. The number of nodes in a tree is relatively small even for an ARA of several thousand elements. For example, if we have six branches at each node, then a tree of only five nodes suffices for an array of 9331 elements. PRR’s are required only at the first through fourth order nodes of this tree. A PRR at a
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