Integrated Mode Composite Transmission Line

In this paper, a novel integrated mode composite transmission line (IMCTL) is proposed, which consists of inner and outer transmission lines. The proposed IMCTL takes full advantages of both substrate integrated waveguide (SIW) and spoof surface Plasmon polaritons (SSPPs) transmission line and supports high-frequency transmission in the inner transmission line and low-frequency transmission in the outer surface transmission line with different propagation modes. The dispersion characteristics of the inner and outer surface IMCTL are studied. The electromagnetic field (EM) distributions and propagation modes of the inner and outer surface IMCTL are examined. The circuit models of the inner and outer surface IMCTL are discussed and analyzed. In order to achieve the transmission of inner and outer surface IMCTL with different propagation modes, two simple high-efficiency conversion structures are utilized to convert the guided waves to the proposed IMCTL. The inner and outer surface IMCTL are designed and simulated, which show good transmission performance. The ohmic losses and dielectric losses of the inner and outer surface IMCTL are simulated and compared with typical transmission lines. The measured data of the proposed IMCTL show a very good agreement with the simulated results. The measured insertion losses of inner IMCTL are within 1.77 ± 0.64 dB from 5.5 to 10.0 GHz and the measured insertion losses of outer surface IMCTL are within 3.21 ± 1.22 dB from 2.0 to 6.0 GHz. The proposed IMCTL will play an important role in the integrated high-performance multiband microwave and wireless communication systems.