Graduation Year

2018

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Electrical Engineering

Major Professor

Thomas M. Weller, Ph.D.

Co-Major Professor

Jing Wang, Ph.D.

Committee Member

Gokhan Mumcu, Ph.D.

Committee Member

Rasim Guldiken, Ph.D.

Committee Member

Thomas Ketterl, Ph.D.

Abstract

This dissertation presents first a comprehensive study of the design and performance of a multilayer dielectric rod waveguide (DRW) with rectangular cross-section. The design is comprised of a high permittivity core encased by a low permittivity cladding. A modal analysis of the multilayer DRW with a 2:1 core aspect ratio is presented and a mathematical model is proposed to characterize the fundamental mode cutoff frequency in terms of the core and cladding permittivity and the core dimensions. The explicit nature of the model is useful for design and it offers an excellent match to the full-wave EM simulation data. The multilayer DRW performance is measured for the extended Ku band (10-18 GHz) considering straight and bent waveguides with different radius of curvature. The multilayer configuration shows a 16.7% and 24% reduction of the 1 dB cutoff frequency for a 10 × 10 mm2 and 20 × 20 mm2 cladding area, respectively, when compared to a single layer design of the same core dimensions. It is also demonstrated that the multilayer DRW shows reduced radiation at the lower end of the band when compared to its single layer counterpart, for different radius of curvature bends. Specifically, the multilayer DRW shows an insertion loss improvement of 9.5 dB at 12 GHz for a 35 mm radii of curvature bend.

In a second chapter, a proposed multilayer DRW designed for the extended Ku band (10-18 GHz) is fully developed and fabricated by using additive manufacturing technologies, particularly fused deposition modeling (FDM). The multilayer DRW is formed by a medium-k dielectric core printed with a custom-made ceramic composite and a low permittivity ABS cladding. Both materials are compatible with FDM. Device performance is measured with and without the presence of the low permittivity cladding. The insertion loss of the multi-layer DRW is less than 0.012 dB/mm and the attenuation due to each waveguide feed transition falls within 0.29 to 0.98 dB in the entire frequency range. Additionally, the presence of the cladding extends the 1 dB cut-off frequency by 2 GHz, thus improving the 1dB operational bandwidth by 50 %.

The effect of a low permittivity cladding used in a multilayer end-fire dielectric rod antenna (DRA) design is studied in terms of return loss, gain and half power beamwidth in the extended Ku band (10-18 GHz). Gain improvement ranging from 4 dB to 7 dB is achieved using cladding permittivities between 1.6 and 2.6 when compared to a single layer design of the same length. For example, a cladding of ϵr =1.6 leads to a peak gain increment of 4.5 dB at 18 GHz and a 20 degree HPBW reduction compared to the non-cladded rod. It is also demonstrated that this design has the same maximum gain as a non-cladded design that is 1.8 times longer. The cladding permittivity in the multilayer DRA can be adjusted to achieve peak performance at different frequencies within the band, while providing gain enhancement in the entire band without reducing the bandwidth.

A multilayer dielectric rod antenna (DRA) design is proposed for mm-wave applications. The multilayer DRA is formed by a medium permittivity dielectric rod core encased by a low permittivity cladding to increase the peak gain. The antenna is fabricated using fused deposition modeling (FDM) of two thermoplastics; a ceramic composite material for the core and acrylonitrile butadiene styrene (ABS) for the cladding. The antenna performance is measured from 30 to 40 GHz and the results are validated using numerical simulations. The peak gain of the multilayer antenna is over 22 dBi for the entire frequency range. The effect of the cladding on the antenna performance is to increase the gain by 3-8.5 dB, with a reduction in the half power beamwidth of 22 degrees at the center frequency. The multilayer DRA design offers high gain performance, scalability to other frequency ranges and low-cost fabrication.

A metal grated pattern was implemented on a dielectric rod antenna (DRA) with rectangular cross-section to increase the antenna gain in a narrowband. The DRA is formed by a high permittivity core that is cut into shape using laser machining. The metal strip loading is added using micro-dispending of silver paste. The proposed design was characterized from 12.4 to 18 GHz, a peak gain increment of 2 dB was measured at 13 GHz and a half power beamwidth (HPBW) reduction of 12 degrees was obtained with metal strip length of 0.27 λg. An improvement that yields ~ 50% reduction in body gradient size when compared to a non-loaded antenna. Simulated data shows the inverse relationship between the end fire peak gain frequency and the strip length.

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