Effect of directional elements on the directional response of circular antenna arrays

The paper analyses the effect of directional elements on circular antenna arrays fed by phase-mode excitations. These phase modes represent a convenient pattern-synthesis technique for circular arrays as they correspond to Fourier terms of the far-field pattern. A serious limitation on circular arrays, when employing omnidirectional elements, relates to rapid variations in the amplitude of the modes due to changes in array diameter or frequency. The analysis shows how the phase-mode synthesis technique may be extended to take account of directional elements. It also reveals that the use of directional elements can overcome the above limitations and can enable circular arrays to synthesise wide-bandwidth directional patterns. The choice of element patterns of the form 1 + cos ¿¿ seems particularly suitable. The analysis also shows that the directional elements can prevent the deterioration of pattern shape with elevation angle (angles away from the plane of the circle).