A Study On Structures Of Millimeter-wave Low-loss Transmission Lines

Planar open structure transmission lines which are easy to connect with other circuit elementsare widely used in the millimeter wave circuit. But operating frequency is high in the millimeterwave circuit, so losses of the conventional transmission lines are very high, which makes the signalsdecay within a short distance. So, to achieve high-performance microwave circuit, we need to takemeasures to reduce losses of transmission lines. It’s principal to adjust the structures of transmissionlines to realize low losses in the development of millimeter wave circuit and system in the conditionthat the properties of materials are not changed. So, we study the characteristics of low-loss planaropen structure transmission lines in this thesis.Firstly, provided that transmission mode stays the same, we make a summary of loss mechanismof different structure transmission lines in terms of the reasons of transmission lines losses;moreover, we also use simulation tools to analyze quantitatively the influence of geometricparameters on losses of transmission lines; finally, we modify conventional CPW and then proposetwo novel low-loss transmission lines, namely, trenched overlap CPW (TOCPW) and innerconductor embedded CPW (IECPW). The attenuation constant of TOCPW with the impedance of50is at least43%smaller than that of conventional CPW at50GHz. The attenuation constant ofIECPW can achieve lower losses (<0.4dB/cm at50GHz).In addition, in this thesis, a qualitative analysis method is proposed to analyze the characteristicimpedance of multi-conductor transmission line versus structural parameters. Although we can’t getthose entire expressions of impedance with this method, we can get impedance against differentgeometric parameters fast and accurately. It provides an intuitive concept. Coaxial line, stripline andcoplanar waveguide are analyzed with this method. And the change rules of characteristicimpedance against structural parameters are the same with that of formulas, which verifies theaccuracy of this method.