Polymer-Based Low-Cost Micromachining of Gap Waveguide Components

Licentiate thesis, 2021

The millimeter-wave (mmWave) and sub-millimeter-wave (sub-mmWave) frequency bands have gained significant attention over the past few years due to the growth of commercial wireless applications. As the operating frequency approaches these higher frequencies, the dimensions of the waveguide-based components continue to decrease. The decreasing feature size of those waveguide components makes the traditional machine-based (computer numerical control, CNC) fabrication method increasingly challenging in terms of time and cost, especially above 100 GHz. Additionally, this method is a serial process and cost will not scale with volume production. Micromachining has the potential of addressing the manufacturing issues of mmWave components. However, the existing microfabrication techniques either suffer from technological immaturity, are time-consuming, or lack sufficient cost-efficiency. A straightforward, fast, and low-cost fabrication method that can offer batch fabrication of waveguide components operating at mmWave and sub-mmWave frequency range is desirable to address the needs for hardware on the growing market of mmWave and sub-mmWave wireless systems.

Conventional metal waveguides have very strict fabrication requirements in terms of mechanical assembly and integration of RF electronics. In comparison, gap waveguide technology not only offers competitive loss performance but also provides several benefits in terms of assembly and integration of active components. A gap waveguide is a planar waveguide technology which does not suffer from the dielectric loss in planar waveguides and which does not require any electrical connections between the metal walls, in contrast to hollow waveguides. This thesis aims to realize gap waveguide components operating at mmWave and sub-mmWave frequency range, in a low-cost and time-efficient way by developing new polymer-based fabrication methods.

A template-based injection molding process has been designed to realize a high gain antenna operating at D band (110 -170 GHz). We can confirm that injection molding of OSTEMER is a straightforward and fast device fabrication method. In the proposed method, the time-consuming and complicated parts need to be fabricated only once and can later be reused.

A dry film photoresist-based method is also presented in this thesis to fabricate waveguide components operating between 220 - 320 GHz. Dry film photoresist offers rapid fabrication of waveguide components without using sophisticated tools. The measurement results presented in the thesis indicate that this dry film-based method is a promising method for fabricating waveguide components operating in mmWave and sub- mmWave frequency ranges.