Abstract

As the communication system goes up to millimeter-wave frequencies for high data rate demands, the conventional microstrip line no longer meets the requirements due to its excessive radiation and harmful surface waves, causing unacceptable insertion loss and interference issues. The radiation and surface waves are absent in the stripline. However, its conductor loss becomes worse due to the narrower strip causing by the implemented two ground planes. In addition, any vertical asymmetry in the stripline can generate unwanted higher order waveguide modes that will be able to propagate wherever the ground planes exist. The standard waveguide technology is not suitable for millimeter-wave bands because of the small dimension of the hole, which causes fabrication challenging and high cost.

The new technology of gap waveguide (GW) offers a solution to the above problems in current guiding structures. Considerable effort is being made to miniaturize it using the printed circuit technology for low-cost and low-profile applications. The microstrip-ridge GW and the inverted microstrip GW are the two candidates reported previously. However, they come with their own drawbacks. The tiny air gap makes it very sensitive to the outside pressure or the environmental factors. The plated vias in the copper strip and the electroless nickel immersion gold (ENIG) coating on the strip cause substantial attenuation and a frequency shift. In addition, it is challenging to connect to other transmission lines or conventional rectangular waveguides for the integration and measurements. Therefore, one major part of this thesis is to develop innovative GW structures without the formerly mentioned issues to be suitable for millimeter-wave frequencies and easier implementation. Another major part is developing passive components, such as antenna arrays, using the proposed new GW structures. The third part is studying the GW-based PMC packaging for the irregular ground/PEC plane. This will help extend this new packaging technology from the microstrip line circuits to the substrate integrated waveguide (SIW)- or grounded coplanar waveguide (GCPW)-based circuits.