Novel waveguide filters in communication systems

Wang, Daxin ORCID: 0000-0003-0400-3113 (2023). Novel waveguide filters in communication systems. University of Birmingham. Ph.D.

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Abstract

This thesis presents the design and fabrication of several waveguide bandpass filters operating at X band (8-12 GHz), V band (50-75 GHz) and WR-1.5 band (500-750 GHz). A WR-1.5 band (500-750 GHz) 3\(^{rd}\) order waveguide bandpass filter has been designed and manufactured using high-precision computer numerically controlled (CNC) metal machining. This filter is used as a prototype to find the tolerance of commercial CNC milling machine. The sensitivity analysis and yield analysis are presented to help estimate the real production and improve the fabrication tolerance. However, the long waveguide section in that filter leads to additional losses. To reduce the loss of waveguide, the filter can be shortened by applying folded structure, which can make the whole structure more compact. Therefore, the filters with folded structure was developed. The folded structure allows a very compact filter with axial connection to waveguide ports. However, the compact structure leads to small bandwidth and increases the difficulty of fabrication. In order to increase the bandwidth, a new coupling structure has been introduced. The bandwidth is increased successfully.

The designs of three-dimensional (3D) printed filters are also presented in this thesis. 3D printing presents attractive benefits such as flexibility in structural and material selection. In contrast to filters fabricated by conventional milling technologies, these two 3D printed filters can be manufactured in a single piece without assembly. To take advantage of the flexibility in structural selection, bent, twisted and triangular resonators are analyzed and applied on the filter. Bend and twist structure can change port orientation and polarization, respectively. In traditional, to realize port orientation and polarization, two components are needed. However, the twist waveguide filter in this thesis can be considered as integration of filtering and polarization change. 3D printing shows great potential for the devices working at 60 GHz or higher frequency. However, the fabrication still requires external support structures to avoid overhang structure. These additional support structures will be no longer needed if the resonators are triangular with appropriate angle range. Therefore, the waveguide filter with triangular resonators are designed. The results show that the triangular resonator can realize self-supporting structure and no more additional internal supporting structure are needed. Because the structure of filter is raised to make sure the filter port is on the middle of the flange, external support structure is still needed under the filter. But it is a relatively easy support structure and requires less support materials.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):