Microsystem technology for microwave applications at frequencies above 100 GHz

Doctoral thesis, 2016

The rapid development of wireless technology today shows an increasing need for electromagnetic components operating at even higher frequencies. Higher frequencies offer wider bandwidth, higher spatial resolution and are needed for technologies such as automotive car radars, wireless media communication and body scanners. The biggest issues with developing high frequency components are the small dimensions needed. With the small dimensions, issues with connectivity and resolution of the structures have become difficult to handle at frequencies above 100 GHz. The most common fabrication method used is micro-milling in brass, however this is limited in its resolution and micro-milling is not a mass production method, thus making it expensive. This thesis aims to realize electromagnetic components at high frequencies, more specific above 100 GHz, with the help of microsystem technology. The thesis covers a background and history of the field, a discussion of the technologies used, and presents the fabricated devices, made with microsystem technology. In this thesis, gap waveguides ranging from 100-325 GHz, gap adapters, and transitions fabricated with microsystem technology have been explored. Three different materials: silicon, SU8, and carbon nanotubes, have been tested as base materials together with a gold surface, for a gap waveguide component. The silicon-based structure performed overall the best, while the SU8 process was less costly, the carbon nanotube based structure was determined to be the lossiest of these realizations. The knowledge obtained from these fundamental structures were used to fabricate and measure a ridge gap antenna prototype. A gap adapter was used to connect to the antenna, to reduce leakage without using damaging screws. The antenna, was fabricated in silicon for 100 GHz. A new transition, based on the knowledge of previous transitions was used to connect the waveguide flange to the feed of the antenna. The ridge gap antenna has a 15.5% bandwidth and a gain of 10.3 dBi matching perfectly the simulated design. The presented work in this thesis shows how microsystem technology can realize mass producible microwave components operating above 100 GHz.