Millimeter-Wave E-plane Transmission Lines in Multi-layer Substrate

In this work, two kinds of millimeter-wave E-plane transmission lines in multi-layer dielectric substrate and their transitions to the hollow waveguide are proposed and investigated. The transmission lines of E-plane SIW and finline in multi-layer dielectric substrate show advantages of low transmission loss and low profile, which are useful to design antennas and circuits in the millimeter-wave band. In the E-plane SIW structure, four dielectric substrates are stacked to compose an E-plane SIW. The utilization of thin dielectric substrates can control the cutoff frequency of E-plane SIW and significantly reduce leakage power of horizontal polarization between via holes. In the finline structure, a planar transmission line in E-plane is constructed by a slot line inserted in the middle metal pattern between two dielectric substrate layers. The finline is bounded within a closed structure composed of double-layer substrate and two rows of via-hole arrangement, therefore, low dispersion and low radiation loss can be expected in the finline performance. Waveguide transitions are designed for both transmission lines. The dimensions of the transitions were optimized by electromagnetic analysis of the finite element method at 76 GHz. Transmission loss of E-plane SIW and finline was 0.47 dB/cm and 0.3 dB/cm, respectively. Insertion loss of the waveguide-to-E-plane SIW transition and the waveguide-to-finline transition were approximately 0.17 dB.