Investigation of reduced surface wave microstrip antennas and one-dimensional leaky-wave antennas for broadside radiation

In this dissertation, three different topics related to antennas are discussed. The first topic involves reducing the surface-wave excitation from microstrip antennas. The second topic involves an investigation of the Ewald method for calculating the one-dimensional periodic Green's function with complex wavenumbers. The third topic is concerned with an investigation of the broadside radiation characteristics of a class of one-dimensional finite-length leaky-wave antennas.Surface-wave excitation from microstrip antennas is of major concern in many practical antenna applications. In this dissertation, the challenge of reducing the surface-wave excitation from microstrip antennas is addressed as the first major topic. The proposed approach is based on a theorem called the reduced surface wave (RSW) theorem. The RSW theorem suggests that by properly selecting the permittivity of the filling material inside the patch cavity, the patch does not excite the dominant TM0 surface-wave mode. Although this theorem has been previously introduced, a validation of this theorem is demonstrated here for the first time by comparing the mutual coupling between a pair of RSW antennas and a pair of conventional antennas.The second topic addressed in this dissertation extends the Ewald method for a one-dimensional (ID) periodic array of point sources in free space to allow for complex wavenumbers this allows the Ewald method to be suitable for the analysis of 1D periodic leaky-wave antennas.The third topic of interest in this dissertation is an investigation of various radiation characteristics of finite-length center-fed 1D uniform leaky-wave antennas (LWAs) designed for broadside radiation. The study focuses on the sidelobe level (SLL), radiation efficiency, gain, and bandwidth of such LWAs. Often the aperture of such LWAs is terminated by a matched load to absorb the vestigial (non-radiated) power. A control of the SLL and an improvement in radiation efficiency is achieved here by terminating the aperture either with a short circuit or an open circuit instead of a matched load. Another important aspect associated with the broadside radiation is the beam-splitting condition this aspect is explored for all the terminations considered. The validity of the results is demonstrated through full-wave simulations using Ansoft HFSS.