Strong Fundamental Rejection in Frequency Doublers at 220–260 GHz Using a 250-nm InP HBT Process

Two frequency doublers operating at 220–260 GHz offer high fundamental rejection in a 250-nm Indium Phosphide (InP) HBT process. A second-harmonic termination technique at the input is adopted in both designs to improve collector efficiency (η) and fundamental rejection. The first of the two designs achieves 6.8-dBm peak output power at 220–260 GHz with −3.3 dB peak conversion gain, 17.7% peak η and more than 29.3 dB fundamental rejection. The second design adopting a novel tunable notch filter for fundamental rejection improvement achieves 1.2-dBm peak output power at 220–260 GHz with −14.4 dB peak conversion gain, 6.7% peak η and >54.7 dB fundamental rejection. To our knowledge, these frequency multipliers demonstrate improved harmonic rejection.