Spectral gaps and radiation characteristics of one-dimensional periodic leaky -wave antennas

This dissertation investigates the propagation and radiation characteristics of a periodic strip-grating leaky wave antenna, in two different forms. The first form is an idealized one-dimensional structure consisting of infinitely long perfectly conducting metal strips printed on the top of a grounded substrate. The second form is a practical implementation of the first, called the dielectric-inset rectangular waveguide leaky-wave antenna. This antenna consists of a dielectric-filled rectangular waveguide where one of the side walls has been replaced by a periodic strip grating, with the top and bottom walls extended to form a parallel-plate baffle region that terminates into a radiating aperture. If the baffle height is sufficiently large, the analysis of the practical dielectric-inset waveguide antenna reduces to a modification of that for the idealized one-dimensional structure, which is performed using a rigorous multimode equivalent network model. Leaky-mode propagation on the idealized strip-grating structure is first investigated, and the frequency region known as the spectral gap is studied in detail. The aperture fields and far-field pattern of the idealized structure excited by a line-source feed are then studied, to examine the physical significance of the leaky modes on the structure. It is observed that the nature of the spectral gap itself depends on whether a second space harmonic does or does not begin to radiate before the main radiating space harmonic reaches forward endfire. The analysis is then extended to analyze a finite-length aperture antenna, fed by a coaxial feed arrangement that allows for either a broadside or a scanned unidirectional beam. Finally, a measurement was performed, which shows fairly good agreement between the calculated and measured patterns for one particular design. The slight discrepancy between the measured and theoretical pattern is attributed to the partial reflection of the leaky wave from the aperture edges. It is concluded that the dielectric-inset rectangular waveguide leaky-wave antenna is a practical antenna for microwave and millimeter-wave applications.