A 165–260 GHz Broadband Frequency Doubler Using “Hourglass-Shaped” Transmission Matching Technology

This letter presents a broadband frequency doubler that covers the 165–260 GHz range. To achieve the broadband matching of Schottky barrier diodes (SBDs), an “Hourglass-shaped” (H-S) transmission line is applied in this work. Compared to the conventional high-low impedance microstrip matching, the “H-S” transmission line adopts an asymmetric taper of microstrip steps, resulting in lower transmission loss of interstage microstrip according to the small reflection theory. Meanwhile, the “H-S” transmission line is carefully designed to achieve a minimum reflection coefficient from SBDs to the output waveguide, which can expand the operating bandwidth. To verify this concept, we fabricated and measured a broadband frequency doubler. Measured results show that the doubler has an efficiency of 6.02%–12.02% covering the 165–260 GHz frequency band under 95–135 mW input power. The peak output power is 14.9 mW at 181 GHz under the 135 mW input power.