Novel planar quasi-TEM transmission line with high isolation and its application to T-junction power divider

摘要

In this study, a novel quasi-transverse electromagnetic (TEM) transmission line (TL) on a single-layer substrate is presented. The proposed structure comprises bilateral metalised vias and two longitudinal slots on the top and bottom plates, respectively. This two-conductor TL separated by the two slots allows the quasi-TEM mode and guarantees high isolation due to the vias which constrain the electromagnetic field. Additionally, the proposed structure provides a remarkable high range of the characteristic impedance, enabling a more flexible design. Furthermore, an empirical analytical formula is derived to calculate the characteristic impedance of the proposed TL adopting conformal mapping, and modified by a polynomial fraction. The transitions to the double-sided parallel-strip line and the microstrip line are proposed with which the propagation constant of this TL is extracted. The comparisons of the far-end couplings of several types of microwave TLs have been provided by the simulation and measurement to verify the isolation property of the proposed TL. Finally, the proposed TL is applied to the T-junction wideband power divider design to demonstrate its practicability. A prototype is fabricated and measured with a wide operating bandwidth from 6.8 to 17.6 GHz.