Research On Ultra-broadband And Low-loss Transmission Line

The emerging millimeter-wave/terahertz applications,such as highresolution imaging,high-speed wireless data links,and short-range radar,require transmission lines(TLs)with ultra-broadband,low attenuation,low loss,and low dispersion performance.This thesis presents a series of ultrabroadband,low-loss,and easy-to-manufacture TLs for high-speed digital circuit interconnect transmission,picosecond interconnect,and highfrequency circuit applications.In addition,the thesis analyzes the working principle,and the correctness of the principle is verified by simulation and experiment.The main research work of this thesis is as follows:1.The thesis proposes an air-filled mode selective transmission line(AF-MSTL)composed of an inverted coplanar waveguide and gap waveguide to solve the problem of high dielectric loss in MSTL.As the frequency increases,the transmission mode converts from the quasi-TEM mode of the coplanar waveguide(CPW)to the TE10 mode of the gap waveguide.The gap waveguide has a stopband characteristic,which improves the tolerance of processing and assembly.The AF-MSTL is fabricated and measured,and the measured results show that the S11 is less than-10 dB and the insertion loss is less than 0.3361 dB/mm from 10 MHz to 110 GHz.2.Aiming at the problem of the conductor-backed coplanar waveguide(CBCPW)suffering from anomalous resonances causing narrow bandwidth and ground coplanar waveguide(GCPW)and mode selective transmission line(MSTL)requiring sidewalls on both sides,the TLs with corrugated edges is designed.The periodic structure applied to TLs is proposed to provide stop-band characteristics in the ultra-broadband frequency,which behaves like metal sidewalls.The periodic structure is proposed to replace metal sidewalls,which solves the problem that planar transmission lines are difficult to process metal sidewalls in the millimeter wave/terahertz frequency band.Three different transmission lines working in the DC-100 GHz range are proposed,and all are experimental to verify the correctness of the theoretical analysis.The CBCPW with corrugated edges(CBCPW-CE)consists of the CBCPW and periodically stubs loaded edges.The impedance of the CBCPW-CE is approximately 50 ohms,allowing it to be directly connected to the electrical measuring equipment without additional transitions.The results show that CBCPW-CE has a broadband performance from 10 MHz to 100 GHz,the S11 is less than-10 dB,the insertion loss is less than 0.0774 dB/mm,and the group delay per unit length is between 3.8 ps-6 ps,with the group velocity dispersion(GVD)less than 0.6 ps2/mm.The CBCPW with sine edges(CBCPW-SE),which contains a series of periodic sinusoidal edge loads,exhibits a stopband characteristic from DC to 100 GHz.The CBCPW-SE is fabricated and measured,with the results showing that the reflection coefficient is less than-10 dB from 10 MHz to 100 GHz.The group delay per unit length is between 3.75 ps-5.1 ps and the group velocity dispersion(GVD)is less than 0.7 ps2/mm.The insertion loss is 0.05078 dB/mm at 100 GHz.A mode-selective transmission line with periodic stub edges is proposed,and a gradient transition is introduced to achieve field and impedance matching,and to achieve quasi-TEM mode at low frequency and TE10 mode at high frequency.The prototype is fabricated and measured,with the experimental results showing that the insertion loss is below 0.1 dB/mm from 10 MHz to 100 GHz,S11 is less than-10 dB,and the group delay is flat,with the group delay per unit length ranging between 3.2 ps and 6.2 ps.3.A novel no-vias substrate integrated coaxial line with broadband and low loss is proposed to overcome the issue of requiring metal side walls in traditional substrate integrated coaxial lines.By adding periodic stubs to the central metal layer to suppress leakages,the proposed transmission line does not require drilling processes.The experimental results demonstrate that the insertion loss is less than 0.14 dB/mm from 10 MHz to 75 GHz,S11 is less than-10 dB,and the measured group delay is flat,with the group delay per unit length ranging between 3.7 ps and 6ps,and group velocity dispersion(GVD)less than 0.6 ps22/mm.4.A slotted rectangular waveguide is proposed to overcome the limitation of the dominant mode bandwidth in a rectangular waveguide.The transmission line is composed of a rectangular waveguide and an inverse slot line,which is analyzed for the working principle and optimized for the design.The bandwidth of the TE10 mode in the slotted waveguide is increased from 60 GHz-120 GHz(66.7%bandwidth)to 60 GHz-155 GHz(88.4%bandwidth).Moreover,a transition structure for the slotted waveguide is designed,which has low insertion loss of 0.68 dB at 155 GHz.