Towards Gap Waveguide Array Antenna for Millimeter Wave Applications

Licentiate thesis, 2016

The millimeter wave frequency range has got a lot of attention over the past few years because it contains unused frequency spectrum resources that are suitable for delivering Gbit/s end-user access in areas with high user density. Due to the limited output power that current RF active components can deliver in millimeter waves, antennas with the merits of low profile, high gain, high effciency and low cost are needed to compensate free space path loss and increase the communication distance for the emerging high data rate wireless systems. In order to move towards the millimeter wave frequencies we need to face significant hardware challenges, such as active and passive components integration, packaging problems and cost-effective manufacturing techniques. The gap waveguide technology shows interesting characteristics as a new waveguide structure. It may be suitable to fill the existing gap between the planar transmission lines, such as microstrip, coplanar waveguide and substrate integrated waveguide and the non-planar hollow waveguides in terms of performance, such as loss and fabrication flexibility at high frequencies. Gap waveguide has a planar profile, and it can be used as low loss distribution network for an antenna array. This thesis mainly focuses on passive components design, in particular array antennas and bandpass filters based on gap waveguide technology. We present several low-profile multilayer corporate-fed slot array antennas with high gain, high effciency and wide impedance bandwidth for the 60-GHz band. The aim of this thesis is to demonstrate the advantages of gap waveguide technology as an alternative to the traditional guiding structures to overcome the problem of good electrical contact due to mechanical assembly with low loss. The main challenge of gap waveguide components is the realization of the textured structure (pin surface) with a cost-effective manufacturing method. Due to the relatively complex pattern and physical dimensions of the textured structure, the fabrication of the gap prototypes introduces a challenging task, especially at millimeter wave frequencies. Therefore, we are continuously searching for effective alternative methods. A fast modern planar 3-D manufacturing method called die-sink Electric Discharge Machining (EDM) is applied for the first time to manufacture a large planar high gain antenna at the 60-GHz band. Measurement results and experimental validation are provided for the presented designs.