3. Circuit Representation and Performance Analysis of Phased Array Antennas Including Mutual Coupling Effects

Phased array antennas have gained a prominent position in the design of microwave and millimetre-wave radio and radar systems due to their beam steering capability. In most cases, such phased array structures are large-scaled and may involve a very large number of radiating elements that are interrelated to each other through certain signal routing, feeding mechanism and geometric arrangement. On the basis of the well-established array theory, the array pattern is calculated by the product of an isolated element pattern and related isotropic array factor. This scheme assumes that voltage (current) excitation for each element is uniform (constant) in amplitude but progressively in phase over the entire array. This assumption is valid only for an infinitely extended array. For a finite array, this assumption is very much questionable because it doesn’t account for array edge effects as well as non-uniform current distribution that depend on the geometry, frequency, and scan angle. This complicated parameter dependence results from mutual coupling effects observable among all elements in the array. It is usually difficult to explain and formulate the mutual coupling phenomenon, which is generally related to the re-radiation of power through neighbouring elements, and/or electromagnetic interaction and surface-wave propagation within the substrate as well as the influence of feeding network.