Tunable 500 GHz sensor system in SiGe technology for gas spectroscopy

A 500 GHz system for gas spectroscopy is presented, which includes an SiGe 4 × 1 transmitter (TX)-array, an SiGe subharmonic receiver (RX) and a 1.9 m-long gas absorption cell. The 120 GHz local oscillators (LOs) of the TX-array and RX are controlled by two external phase-locked loops (PLLs), whose reference frequencies are swept. The TX involves a frequency quadrupler. The RX uses a frequency doubler for the 120 GHz LO frequency, which is connected to a subharmonic transconductance mixer. The absorption spectrum of a gaseous mixture of methanol and acetonitrile is measured from 495 to 497 GHz.