Study of Planar Microstrip-to-Waveguide Transitions in Millimeter-Wave Band

Nowadays, more and more technologies are implemented in vehicles to improve driver assistance in order to enlarge comfort and avoid accidents. Automotive radar systems have been gradually installed into vehicles with the growth of wireless technologies. Among the utilizations of automotive radar systems, survey around automobiles for the prevention of traffic accidents is one of the prospective applications. Especially, in the millimeter-wave automotive radar systems, the microstrip antennas are superior candidates when radar sensors are widely used in vehicle due to its advantages of low cost and low profile. Generally microstrip antennas are placed on the surface of the radar sensor and are connected to millimeter-wave circuits inside of the sensor via waveguides. Therefore, transitions from waveguide to microstrip line are required and their key devices. Furthermore, transitions were one of the important devices which connect different types of transmission lines used to transport millimeter-wave signals for not only millimeter-wave radar systems but also many other millimeter-wave systems. Various types of microstrip-to-waveguide transitions have been proposed. Among them, proximity coupling type transition composed of only a single dielectric substrate, has an advantage of low cost and low profile and suitable for mass production. Many functions are required for the transitions such as bandwidth or insertion loss or free arrangement of the microstrip line and so on. However, there are many kinds of iii technical problems because of the complex electromagnetic field distributions of the transition. In this doctoral dissertation, the shape of the patch element of the transition which contributes coupling to the microstrip line is focused as an important structure. Throughout my study, the structure of the patch element of the transition is investigated and controlled suitable for individual applications. By modification of the shape of the patch element, current on the patch element is controlled and various new functions of the transitions are investigated and proposed. Four novel microstrip-to-waveguide transitions are demonstrated; broadband microstrip-to-waveguide transition using waveguide with large broad-wall, narrow-wall-connected microstrip-to-waveguide transition, transition from waveguide to two microstrip lines with slot radiators and microstrip-to-waveguide transition using no via holes. These transitions are designed and fabricated around 77 GHz and 79 GHz band. This dissertation consists of seven Chapters. In Chapter one, target applications of the study are introduced. In Chapter two, Technologies of transmission lines and overview of former developed transitions are summarized. In Chapter three, the first transition structure, broadband microstrip-to-waveguide transition using waveguide with large …