A High-Power G-band Schottky Local Oscillator Chain for Submillimeter Wave Heterodyne Detection
Local oscillator (LO) sources with sufficient output power are indispensable modules in submillimeter wave heterodyne detectors. In this work, we report on the design and characterization of a ×6×2 frequency multiplier chain that covers 176-196 GHz band. The LO chain mainly includes a W-band active times-6 frequency multiplier, a commercial W-band isolator, a W-band power module, a W-band band-pass filter (BPF) and a varactor-based G-band power-combined frequency doubler. First of all, design and performance of the W-band sextupler (×6), power module and BPF are briefly introduced. This is followed by a detailed description of the G-band frequency doubler as the key content. The final stage doubler employs two 50 μm thick quartz circuits and two commercially available varactor diodes. A circuit scheme named power-combining frequency multiplication is used for the doubler design. This circuit scheme is able to double the power handling capability of the frequency multiplier compared to the un-combined one. Therefore, the final stage doubler can fully make use of the driving power delivered by the power module to increase the output power. Each module is fabricated and assembled, and the discrete modules and the cascaded chain are measured, respectively. At room temperature, when pumped with 0 dBm at Ku-band, the LO chain produces at least 12.5 dBm in the 172-196 GHz band with a measured peak power of 16 dBm at 178 GHz. This power level is sufficient to pump a 0.36 THz heterodyne detector and makes it possible to deploy multi-pixel heterodyne imaging arrays in this frequency range.