A High-Power AlGaN/GaN Nonlinear Transmission Line Frequency Comb Generator With Stable Multiplication Efficiency

In this article, an innovative nonlinear transmission line (NLTL) is presented to obtain a high-power frequency comb. A stable efficiency is realized by introducing quasi-stepped capacitance into the NLTL, where the power of the output frequency comb can be continuously raised with the increase of the input power. AlGaN/GaN Schottky barrier diodes (SBDs) with quasi-stepped capacitance are used to compose the NLTL. With an input frequency of 4 GHz, a series of frequency comb from 4 to 24 GHz is generated. The output power varies linearly with the input power range of 15–35 dBm and the harmonic power at 20 GHz is 0 dBm at the input power of 35 dBm. The NLTL saturates at a higher input power, which is caused by the forward-conduction characteristics of AlGaN/GaN SBD, and the saturation power can be improved by depositing a dielectric layer under the anode of SBD. An NLTL-based frequency comb generator is designed utilizing an SBD with a cutoff frequency of 270 GHz. Under a 4 GHz input signal, the 50th harmonic exhibited stable efficiency at −40 dB, showing its potential for terahertz sources, broadband heterodyne receivers, and high-frequency sampling circuits.