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# Micromachined millimeter wave circuits

Ph.D. thesis, University of Birmingham.

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## Abstract

This thesis presents the design and characterisation of millimetre-wave Butler matrix beamforming circuits at 63 GHz. A micromachining technique is used to fabricate the tiny structures. The ability to manufacture the circuits at this frequency may benefit to the development of intelligent transport system (ITS) communication and sensing systems. All components that build the Butler matrix beamformer are designed to fit the thick SU-8 photoresist micromachining technology, where structures are built by bonding together five layers of metal coated SU-8. The matrix is constructed using air filled rectangular coaxial lines. The dielectric losses are avoided by having air filled structure, however the suspended lines need supporting system. Therefore, stubs are placed in the circuits to hold the suspended lines. In order to transfer signal from the Butler matrix to the antenna, a transition is necessary. A rectangular coaxial line to ridge waveguide transition is designed to feed the H-plane horn antenna and the ridge waveguide slot antenna. The novelty of this work is in both the design of new microwave structure and also in the demonstration of millimetre wave structures in micromachined form using SU8 resist. Four new microwave structures are (1) a back to back rectangular coaxial line to ridge waveguide transition, (2) an H-plane horn antenna, (3) a ridge waveguide slot antenna, and (4) a Butler matrix with a patch antenna array. These and other structures have been built and tested and finally the selection put together to form a new type of Butler matrix. The compatibility of the designs to the fabrication method has been demonstrated. The transition return loss is better than -12 dB from 60 GHz to 90 GHz and has been proven to work with integration to the horn and the waveguide slot antenna. The Butler matrix with a patch antenna array exhibits the forming of the beams at $$\pm$$17$$\circ$$ as expected from the theoretical calculation.

Type of Work: Ph.D. thesis. Lancaster, M.J. Colleges (2008 onwards) > College of Engineering & Physical Sciences School of Electronic, Electrical and Computer Engineering T Technology (General)TJ Mechanical engineering and machineryTK Electrical engineering. Electronics Nuclear engineering University of Birmingham 1649
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.

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