Graduation Year

2020

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Electrical Engineering

Major Professor

Gokhan Mumcu, Ph.D.

Committee Member

Kenneth H. Church, Ph.D.

Committee Member

Jing Wang, Ph.D.

Committee Member

Thomas M. Weller, Ph.D.

Committee Member

Ying Zhong, Ph.D.

Keywords

3D printing, antenna arrays, microstrip antennas, packaging

Abstract

This dissertation presents high-performance transmission lines, antennas, and phased arrays with novel packaging techniques by harnessing design flexibilities of additive manufacturing (AM). AM enables realizing multilayered RF electronics with complex geometrical structures that are not practical using conventional fabrication methods. Design flexibilities offered by AM as customized dielectric shapes/thicknesses, dielectric properties, metallization on conformal surfaces, and structural packaging are harnessed for multilayered RF applications. Although several works demonstrated the viability of AM for antenna realizations, its capability for addressing the needs of wideband, high radiation efficiency antenna systems packaged with active RF circuit components remains relatively unexplored. The first major contribution of this dissertation is the 3D printed wideband high-efficiency dual-polarized stacked patch antenna with embedded Monolithic Microwave Integrated Circuit (MMIC) switch. Specifically, dual-polarized antenna bandwidth is enhanced to cover the entire Ku-band by resorting to stacked patch layers, customizing substrate thicknesses, and infill ratios. Switch integration to select polarization is performed with 3D vertical transitions to achieve high return loss and small packaging. To retain a high radiation efficiency and enable future antenna array applications, a detailed investigation is also carried out to maximize the performance of microstrip feed lines by adjusting the substrate thickness, infill ratios, and deposition directions. The presented Ku-band antenna consists of five conductive and eight dielectric layers realized with a single AM platform and offers state-of-the-art performance. Specifically, to the best of our knowledge, the dissertation demonstrates the lowest attenuation in the literature for a fully printed microstrip line with 0.25 dB/cm measured insertion loss at 18 GHz. The antenna operates with more than 80% radiation efficiency and 45% impedance bandwidth. The antenna retains a low cross-polarization ratio of 20 dB due to 3D feed line transitions and symmetric location of the embedded switch with respect to the antenna feed points.

Wideband aperture-patch antenna using DDM can be extended to phased array antennas installed on small or conformal platforms, which requires low back radiation and structurally integrated electronics compared to traditional bulky packaging. The second major contribution of this dissertation the demonstration of an X-band phased array antenna element with an embedded cavity and a MMIC phase shifter. Printing direction should be from base to the antenna to allow for printing on planar/conformal platforms. The cavity is embedded under the coupling aperture to increase the front-to-back ratio. A MMIC phase shifter in QFN package is fully embedded inside the substrate for packaging within a small unit cell. For characterization, the embedded microstrip feed line is transitioned to exposed CPW using selective FDM technique. The antenna exhibits 81% radiation efficiency (excluding IC loss) and 23% impedance matching bandwidth without the phase shifter. Embedded cavity over the coupling aperture of the patch antenna increases the front-to-back ratio to >20 dB. Return loss of the antenna with phase shifter is more than 10 dB within the operating bandwidth for different phase shifter states. The phased array antenna element is suitable for half-wavelength spacing. The design is implemented to a 2x2 sub-array with the addition of layers and shift registers to perform the signal, control, and bias line routing.

Microdispensed transmission lines (TLs) are known to show high conductor losses at microwave frequencies due to the low conductivity of silver inks and pastes, non-uniform crosssections, and high surface roughness. Recently, laser micromachining has been introduced as a technique to improve the conductivity of coplanar waveguide (CPW). By laser micromachining the slots of the CPW, smoother, and highly conductive signal trace and ground plane edges have been obtained and shown to enhance effective conductivity. So far, this enhancement has only been shown with CPW. Since conductor loss depends on the TL type and geometry, the effect of laser micromachining on other TL types should be investigated. The third major contribution of this dissertation is the demonstration of laser micromachining for microstrip and grounded coplanar waveguide (GCPW) for the first time, and improvement of their conductivities within the 1 GHz – 30 GHz frequency range. Specifically, laser micromachining is shown to decrease insertion loss at 30 GHz by 0.18 dB/cm and 0.29 dB/cm for the microstrip and GCPW, respectively, when the TLs are over a 254 micrometer thick substrate 3.6 dielectric constant. Effective conductivity of laser micromachined microstrip line and GCPW are extracted as 5 MS/m and 12.5 MS/m at 30 GHz, respectively. It is shown that GCPW benefits from laser micromachining the most due to higher current concentration at the signal trace edges. Narrower lines are also shown to improve the most with laser micromachining.

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