Bandwidth Enhancement of Antenna Arrays Utilizing Mutual Coupling between Antenna Elements

Antenna arrays are widely used in many practical systems to enhance gain or provide beam scanning capability. Mutual coupling between antenna elements is an important issue in designing antenna arrays. It modifies radiation pattern, beamwidth, and directivity of an array, and even degrades the performance of adaptive arrays. However, Ludwig demonstrated that mutual coupling is a natural and desirable effect in array behavior, and there is an optimum nonzero value of mutual coupling and passive reflection coefficient, which yields maximum array gain for an array in the active mode. It is also well known that the driving-point impedance of elements in an array with all elements excited depends upon the self-impedance, the mutual impedance, and input current relations between elements.