Abstract
This thesis examines the radiation pattern characteristics of microstrip linear travelling-wave array antennas. Initial experimental investigations indicate that these structures can, in some circumstances, suffer from severe polarisation impurity particularly in the off-axis planes. These performance limitations have not been reported in the literature prior to this work, and are not amenable to calculation by existing theories. With the objective of accurate radiation pattern calculation of generalised periodic microstrip travelling-wave array structures, a new, unified, theoretical treatment is developed. This theory is based on a Green's Function formulation in an infinite array environment. In this way, higher order effects such as mutual coupling, surface wave generation and hybrid-mode propagation are included. Additionally, the analysis is structured to enable a wide variety of antenna geometries to be considered. Each non-identical period of a practical array is considered as being in an infinite array of identical periodic geometry. This geometry is then specified in terms of a single period (or "unit cell"). The unit cell geometry of the array to be studied is specified as a set of non-equal rectangular segments whose dimensions and positions are variable. In a numerical implementation of the analysis, this allows the geometry of the antenna to be specified at run-time. Application of the infinite array results to practical, non-infinite structures is discussed, and the resultant radiation patterns calculated via a suitable Green's Function. This theoretical approach is validated by comparison between experimental and predicted results. Very good correlation is obtained although in short (10 wavelength) structures, direct radiation from the transition effects the experimental results. In both the general applicability and the accuracy of the results, the theory appears to be a significant advance in the analysis of this class of radiating structures.