LAUSR

This paper presents a low-loss and broadband impedance-interface waveguide and a broadband mode-matching technique to convert transverse electromagnetic (TEM) mode into line-wave (LW) mode, which is formed at the interface between two complementary impedance surfaces. Furthermore, an ultra-wideband Y splitter is designed based on the one-dimensional (1D) impedance-interface waveguides. Broad bandwidth, low loss, tunable mode confinement, and ability for integration are the benefits of 1D impedance-interface waveguides. However, their drawbacks may stem from the lack of and problematic excitation of a pure LW mode at the interface between two planes. Another limitation is the coupling efficiency between 1D impedance-interface waveguides and conventional microwave waveguides. To ratify such limitations, a broadband tapered-slot Vivaldi transition is designed to excite the proposed 1D impedance-interface waveguide. Subsequently, a Y splitter consisting of complementary impedance surfaces is designed, fabricated, and measured. The Y splitter is implemented in the frequency band of 4--16 GHz, having a bandwidth of $120\mathrm{%}$ and an insertion loss of approximately 1 dB. The aforementioned characteristics of 1D impedance-interface waveguides are fully verified. Consequently, the proposed waveguide, mode-matching technique, and Y splitter could be used for the design of other microwave devices.