In this article, a novel waveguide reconfigurable Schottky diode-based frequency doubler with tunable multiband high efficiency output is proposed and demonstrated. The multiband frequency output is achieved by reconfigurable input waveguide matching and cross-band output circuits matching. In the doubler, the whole cavity is composed of two parts: reconfigurable input matching waveguide cavities and coused main circuit associated with the coused cavity. These reconfigurable cavities are designed to match input impedance for corresponding band. The coused main circuit is adopted by weight optimization to fulfill output match of multiband. Then, the reconfigurable cavity is assembled into doubler through reduced-height waveguide choke flange, which aims to alleviate the assembly interconnection losses. Sample of the frequency doubler, operating at 170, 183, and 220 GHz, has been demonstrated based on this prototype. Measured results indicate that, the peak efficiencies of three bands are 38%, 34.5%, and 22.3%, respectively, with a total tunable operating bandwidth of 50 GHz.

In this paper, a high-power 170 GHz frequency doubler based on a Schottky diode is proposed using an in-phase power-combining structure. Unlike a conventional power-combining frequency doubler, the proposed frequency doubler utilizes the combination of a T-junction power divider and two bend waveguides to eliminate the phase difference between the two output ports of the T-junction power divider, so as to achieve in-phase power combining with a concise structure. The frequency doubler was fabricated on a 50 μm thick AlN high-thermal-conductivity substrate to reduce the impact of the thermal effect on the performance. The measured results show that the doubler exhibits a conversion efficiency of 11–31.3% in the 165–180 GHz band under 350–400 mW of input power, and a 118 mW peak output power with a 31.3% efficiency was measured at 174 GHz `when the input power was 376 mW. A good agreement was achieved between the simulation results and the measured performance of the doubler, which proves the effectiveness of the proposed in-phase power-combining structure.

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.

To address the requirement of functioning as a transmit/receive isolation device in terahertz transceiver systems, in this paper, we present two high−isolation multi−branch waveguide directional couplers operating at a center frequency of 510 GHz. One is a high−performance five−branch directional coupler, and the other is a new type of three−branch waveguide coupler with lower processing difficulty. Both couplers were fabricated using low−cost CNC milling technologies. The performance of these couplers was verified through measurement results, demonstrating high isolation at the center frequency.