Sadia Farjana, Electronic Materials and Systems Laboratory

Opponent: Dr. Goutam Chattopadhyay, NASA Jet Propulsion Laboratory
California Institute of Technology, Pasadena, California, United States

Main supervisor: Prof. Per Lundgren

Examiner: Prof. Johan Liu

Abstract:
The terahertz (THz) frequency bands have gained attention over the past few years due to the
growing number of applications in fields like communication, healthcare, imaging, and
spectroscopy. Above 100 GHz transmission line losses become dominating, and waveguides
are typically used for transmission. As the operating frequency approaches higher frequencies,
the dimensions of the waveguide-based components continue to decrease. This makes the
traditional machine-based (computer numerical control, CNC) fabrication method increasingly
challenging in terms of time, cost, and volume production. Micromachining has the potential
of addressing the manufacturing issues of THz waveguide components. However, the current
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 THz frequency range is
needed to address the requirements.

A gap waveguide is a planar waveguide technology which does not suffer from the dielectric
loss of planar waveguides, and which does not require any electrical connections between the
metal walls. It therefore offers competitive loss performance together with providing several
benefits in terms of assembly and integration of active components. This thesis demonstrates
the realization of gap waveguide components operating above 100 GHz, in a low-cost and time-efficient
way employing the development of 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). The injection molding of OSTEMER is an uncomplicated
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 for the fabrication of waveguide
components operating above 100 GHz. Dry film photoresist offers rapid fabrication of
waveguide components without using complex and advanced machinery.

For the integration of active circuits and passive waveguides section a straightforward solution
has been demonstrated. By utilizing dry film photoresist, a periodic metal pin array has been
fabricated and incorporated in a waveguide to microstrip transition that can be an effective and
low-cost way of integrating MMIC of arbitrary size to waveguide blocks.

Keywords: Antenna, Dry film photoresist, Gap waveguide, Injection molding, MEMS,
mmWave, Polymer microfabrication, Terahertz frequency, Waveguide.