Directional pattern synthesis in circular arrays of directional antennas
This thesis describes a mathematical and experimental study of circular arrays of directional antennas. For directional pattern synthesis in circular arrays of omnidirectional elements, mode-analysis or Fourier harmonic analysis technique has previously been used. This thesis describes the effect of using any directional element on the mode properties - in the horizontal plane, and on the vertical directional pattern of such arrays. The effect of random amplitude and phase errors in the excitation of circular arrays and of mutual coupling with reference to directional pattern synthesis is also studied. A procedure is outlined for designing circular arrays of directional elements and a design of an experimental 16- element circular array is then presented. This is an 8 foot diameter array of 16 wideband elements each having a pattern of the form (l+cosφ) for operation at 200-400MHz frequency band. Various mode patterns are computed for the array to determine their purity. The theoretical wideband performance of the array is also examined. New techniques are described for the synthesis of single and 2n sharp nulls in otherwise omnidirectional patterns of circular arrays and the mechanism for independent steering of these nulls is also described. Patterns are computed to demonstrate and theoretically study the techniques. Finally, experimental results are presented to complement the theoretical study of circular arrays and null patterns.