Ridged Substrate Integrated Coaxial Line for Wideband Millimeter-Wave Transmission

In this article, a ridged substrate integrated coaxial line (RSICL) is proposed, which has a compact size, wide bandwidth, and excellent shielding. The RSICL has two ridges set on both sides of its outer conductor, which introduce additional capacitance and enhance shielding performance. Compared with the SICL, the width of the RSICL can be reduced significantly for 50- Ω characteristic impedance. Hence, the monomode bandwidth of the RSICL is larger than that of the SICL. Closed-form formulas based on the conformal mapping method are derived for fast calculation of the characteristic impedance of the RSICL. Compared with full-wave simulation, the proposed formula has an error of less than 1%. An RSICL with grounded coplanar waveguide (GCPW) transitions is designed and fabricated under print circuit board (PCB) technology. The measurement results show the RSICL with the transitions has a bandwidth from dc to 40 GHz, insertion loss less than 1.9 dB, return loss larger than 10.5 dB, and a data rate of 32 Gb/s with a good eye diagram and low bit error rate (BER). The measured attenuation of the RSICL is 0.021 dB/mm at 40 GHz. Full-wave simulation results show that the width of the RSICL is 6% smaller than that of the SICL, the monomode bandwidth is 6.7% wider, and the energy leakage of the RSICL is only 1/120 of the SICL.