A spiral-doublet scanning array

An array of eight spiral doublets, each doublet consisting of a pair of equally-excited two-wire spirals in the same plane and wound in opposite senses, has been used to scan a beam of horizontal polarization over a range simply by rotations of the spiral doublets. The combination of a microstrip ring network and twin lead provided a balanced feed for each spiral in the array. Sidelobe levels were those predicted (25 db) for the broadside pattern and-at the test frequency of 1430 Mc-were, in general, below 19 db over the scan. A novel microstrip feed harness provided isolation between the doublets and served to absorb most circulating currents. This printed circuit feedboard consisted of judiciously-grouped microstrip ring networks and provided the desired feeding coefficients to within db. An application of the array for tracking purposes is also described.