Dielectric Waveguides for Electromagnetic Band Gap (EBG) Structures, Antennas, and Microwave Circuits

摘要

Dielectric waveguide structures, formed using rectangular blocks of dielectric, can guide electromagnetic energy in a frequency range suitable for new microwave antennas and devices, or between 2 GHz and 18 GHz. In this thesis, we present the analysis and design of thin dielectric waveguide structures so small that for the first time, they can be made economically out of readily available substrates, or circuit boards, even at these frequencies. These strikingly thin metallic-bound dielectric waveguides (H-guides), to be operated in a single fundamental mode, are analyzed and subsequently applied to three brand new applications: a square periodic H-guide structure, an antenna, and a thin H-guide dual-directional coupler.ududIn the first application, we investigate periodic dielectric structures, or Electromagnetic Band Gap (EBG) structures, where a new model for periodicity applies thin H-guide transmission lines with discontinuities. This model allows for the resonant frequency, transmission (S21), and reflection (S11) parameters of such structures to be found quickly and quite accurately with closed form expressions, without the need for any numerical methods. As an added benefit of the new model, which can be represented as a z-transform, an inverse operation exists, creating the possibility to design a structure that meets a certain frequency response.ududIn the second application, we explore the use of the thin H-guide as a transmission line feed for a new type of aperture horn antenna that is not only high gain, but also wideband. Incredibly, with proper design, the antenna can also meet low-sidelobe levels between frequencies of 8 and 18 GHz. The proposed thin H-guide aperture horn antennas have wider bandwidths than typical array designs, have similarly high gains as compared to traditional air-filled horn antennas, and can even be easily fabricated using typical two dimensional substrate machining processes. The prototype operates from 8 to 18 GHz with a peak gain of about 18 dBi with reference to the H-guide transmission line.ududTo make antenna fabrication and measurement of periodic dielectric structures possible, a new transition based on microstrip design has been carefully developed that exceeds the performance of all previous microstrip to dielectric waveguide transition designs. This wideband, low loss, Bézier-shaped microstrip to thin H-guide transition has been carefully developed and is discussed in detail in this thesis. This transition can even be fabricated using the same two dimensional substrate machining processes used for the H-guide aperture horn antenna, which allows for the seamless integration of the two structures.ududFinally, a dual-directional H-guide coupler is discussed that is much thinner than air-filled waveguide designs. The structure is so thin that its total thickness can be less than 2 millimeters, where the design obtains a directivity of better than 25 dB over a large bandwidth of 8 to 14 GHz.ud