Research On Passive Devices Based On Rectangular Micro-coaxial Process

With the rapid development of wireless communication technology,millimetre wave integrated circuits are moving towards multi-functional chips on the wafer level,which deepens the demand for passive devices with high precision,easy integration,ultra-low loss and unaffected by radiation.With recent advances in microelectromechanical system(MEMS)manufacturing technology,various types of surface micromachining techniques have contributed to high-precision three-dimensional rectangular micro-coaxial processes with sub-millimetre dimensions.On the one hand,it processed by sequential deposition of metals on wafer-level silicon,making it suitable for interconnecting with high-density integrated circuits.On the other hand,the rectangular micro-coaxial line,as an air-filled metal transmission line,is suitable for high operating frequencies and has the advantages of low loss,low line-to-line crosstalk and ultra-low dispersion.In this thesis,two microwave passive devices are designed based on a novel micro-coaxial process,realizing the advantages of device miniaturisation and low loss.The main work of this thesis is as follows:(1)Firstly,the background and significance of the research on rectangular micro-coaxial transmission line are introduced.Then,based on theoretical analysis and modelling simulations,the transmission mode,impedance characteristics and transmission properties of the rectangular micro-coaxial transmission line are discussed and analysed and a comparison with the three traditional transmission lines of microstrip line,stripline and grounded coplanar waveguide shows that the micro-coaxial transmission line has the advantage of maintaining extremely low insertion loss in the broadband range,especially at high frequencies(0.067 dB @ 50 GHz,0.093 dB @ 100GHz).(2)A novel stacked 4 × 4 Butler matrix has been designed using rectangular micro-coaxial process.Each channel of the Butler matrix is constructed with a 5-layer process and the channels are stacked two by two in a folded form,resulting in a compact 4 × 4 Butler matrix based on a9-layer process in the 24 ～ 32 GHz band with low insertion loss and low phase imbalance.Then,based on the above structure,a beam scanning micro-coaxial antenna array with is designed.The simulation results show that the proposed antenna array has a broadband characteristic of 25.3 ～ 31 GHz.At the same time,the antenna array has good beam formation performance and high beam symmetry over the whole frequency band.(3)Based on transmission line theory,a 4-way coupled-line wideband equal-split Wilkinson power divider has been designed and processed by using rectangular micro-coaxial transmission line.Its operating band is from 6 to 18 GHz and has a compact dimension of 23.5 mm × 14.46 mm× 0.9 mm.The simulation results show that the maximum insertion loss of this structure is 0.42 dB over the entire band,while the isolation is better than 16 dB,and the return loss of ports is better than 13.5 dB.Measurement results are in accordance with the simulation ones,showing that the proposed power divider is suitable for microwave communication system.