Gap Waveguide for High Frequency Microwave Application- Validation of Concept, Filter Design & Packaging Aspects

Licentiate thesis, 2011

The overall goal of this thesis is to validate the low loss performance of recently evolved gap waveguide technology and to use this low loss technology for designing critical passive microwave component such as narrow band filter. Also, the exploitation of gap waveguide concept as a packaging solution for densely packed RF circuitry has been presented in this thesis. Though all the studies presented in this thesis are in Ku band, still the gap waveguide technology is more suitable for high frequency microwave applications. Interconnect problems; packaging problems and also the critical manufacturing issues of radio front-end components have been the major limitations towards using the mmWave technology for regular commercial applications. The proposed gap waveguide technology is proven to be better in many of the above mentioned problem areas and therefore, it is worthy of doing more research on this topic. There are some key issues to be considered while using conventional microwave technologies such as planar microstrip line or the metal waveguide for building up high frequency microwave module or systems. At first, this thesis explains these factors briefly and put forward the existing performance gap between the planar transmission lines such as microstrip or CPW and the non-planar metal waveguides in terms loss, manufacturing flexibility and cost. The packaging problems in conventional microwave circuitry are also brought up from practical view point. After that, the newly proposed gap waveguide technology is presented as a promising solution for high frequency microwave problems. The operating principle of the proposed gap waveguide technology is explained along with design of the parallel plate stop band. Measurement results for the manufactured gap waveguide demonstrators are also provided with details of loss analysis. Moreover, the parallel-plate stopband obtained from PMC surface and smooth metal surface is utilized as a new packaging solution for high frequency RF circuitry. The basics of new PMC packaging along with some experimental verification are also stated in this work. Finally, mechanically flexible design of high Q groove gap resonator and groove gap filters are discussed. Narrowband filter design with 3rd order and 5th order chebyshev response is presented and this opens up whole new idea of designing filters without problematic electrical contact between split blocks and sidewalls.