Abstract :
The paper describes in a tutorial fashion the excitation, near- and far-field radiation characteristics of a particularly simple three to six-element circular array having a steerable notch in an otherwise azimuthal omindirectional pattern. This "notch" radiation pattern can therefore find application in a hand-held terminal where it is desirable to minimize field radiation in the immediate vicinity of the user´s head. It is also feasible to provide two independently steerable notches from an array of four or more elements. Whilst one notch is pointed in the direction of the user the other notch(s) may be used to minimize interference with/from other instruments having overlapping frequency bandwidths. The arrays considered here consist of N identical, parallel, nonstaggered, centre-driven elements that are equally spaced about the circumference of a circle. This means that the elements are at the vertices of an N-sided regular polygene. The basic symmetry of circular arrays offers a number of advantages, which in addition to the 360/spl deg/ scan angle can include an ability to compensate for the effects of mutual coupling by breaking down the array excitation into a series of symmetrical spatial components. This can also give rise to directional patterns which remain constant in shape over broad bandwidths. These advantages together with convenient digital array phasing are particularly suited for mobile cellular phones operating at frequencies of 900 MHz to 2 GHz and similar futuristic applications at higher frequencies up to say 60 GHz.
