In this paper, a novel three-dimensional integrated spoof surface plasmon polaritons (SSPPs) transmission line (TL) is proposed. The controlled slow surface wave can propagate along unit cells that are planted on a metal strip periodically, which is similar to the typical SSPPs TLs. The dispersion characteristics and high-order modes of the proposed TL are studied. In order to verify the transmission performance of the proposed TL, a two-dimensional (2D) structure is utilized to do like the conversion. We have designed the proposed TL and give the simulated results from 10-25GHz, which show good propagation performance. The ohmic losses and dielectric losses of the proposed TL and typical 2D SSPPs TLs are simulated and compared with the microstrip line, coplanar waveguide. The measured data for the proposed TL indicates that the measured results are close to the simulations. The low-loss and highly integrated characteristics of the proposed TL plays an important role in the microwave and terahertz SSPPs transmission and integrated circuits. INDEX TERMS Spoof surface plasmon polaritons (SSPPs), dispersion characteristics, high-order modes, loss characteristics.

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.INDEX TERMS Mode composite transmission line, spoof surface plasmon polaritons (SSPPs), substrate integrated waveguide (SIW), dispersion characteristics, circuit models, loss characteristics.

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In this letter, odd-mode and even-mode spoof surface plasmon polaritons (SSPPs) supported by complementary plasmonic metamaterial with underlayer ground are investigated. The dispersion characteristics and electric field distributions of the odd-mode and even-mode SSPPs are studied. Different high-efficiency conversion structures are proposed to realize the excitation of odd-mode and even-mode SSPPs transmissions. The odd-mode and even-mode SSPPs transmission lines are simulated and measured. The measured insertion losses of odd-mode transmission line are within 2.58 ² 1.23 dB from 3.0 to 10.0 GHz. The measured insertion losses of even-mode transmission line are within 1.66 ² 1.18 dB from 2.0 to 12.0 GHz. The simulation and measurement results validate the highefficiency excitation and excellent propagation performance of odd-mode and even-mode SSPPs on the complementary plasmonic metamaterial with underlayer ground in the microwave frequencies.

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