Phase compensation of organ pipe antenna feeds

Electromechanical scanners such as an organ pipe with a sectoral horn output have proven themselves to be excellent devices for rapidly moving a radiating phase center through the focal region of a collimating reflector system thereby causing the far-field beam of the total antenna to be scanned. The configuration of the radiating outputs of the scanner channels are constrained by the following two independent and often conflicting requirements: firstly, the contour must conform to the scan are required by the particular antenna geometry, and secondly, the peak of the primary feed pattern should aim approximately toward a specified point at all scan angles. Since equal length channels fed in-phase radiate along the normal to their output contour, the scanner usually cannot meet both of these requirements simultaneously. A method is described in this paper for phasing each individual channel of the scanner so as to meet both requirements. Since the technique is indeed frequency dependent, a bandwidth analysis is performed. Both theoretical and experimental data are presented which indicate that the method is sufficiently broadband to find practical application. The implementation of the method described herein should allow antenna engineers much more flexibility in the design of scan arcs for electromechanically scanned antennas.