A 140–220-GHz Balanced Doubler With 8.7%–12.7% Efficiency

In this letter, a 140-220-GHz balanced doubler with high efficiency is presented. To implement the proposed doubler, a taper-type balun is introduced based on a metal ridge, which features an exponential and n-order sine power fitting function. Such a ridge with a slot feeds the input signal to the T-type diodes with the equal magnitude and reverse phase. Then, the second harmonic can be extracted by the metal fin-line transition. To ensure the second harmonic transmitting to the output port, an air bridge across the ridge is utilized, which is close to the diodes with a quarter-wavelength (λ/4) of the center operated frequency fc. Comparing to conventional doublers, the proposed design without substrate eliminates the dielectric loss and substrate parasitic for the enhanced efficiency with an extended bandwidth. To verify the above-mentioned mechanisms, a wideband doubler is fabricated and measured, which exhibits a good efficiency from 8.7% to 12.7% at 140-220 GHz.