Simultaneous Time and Frequency Domain Characterization of a Superheterodyne Terahertz Communication Frontend

The simultaneous in-situ measurement of the complex transfer function under the presence of wideband modulated communication signals in a 300 GHz transmit-receive frontend is presented, allowing for mapping of time domain signal quality measures like error vector magnitude to the nonlinear frequency domain magnitude and phase characteristics of the terahertz transceiver. Arbitrary digital modulation schemes can be superimposed with the injection of vectorial test signals. The paper shows how the frequency domain transfer function is affected by the presence of a 16-QAM modulated signal with 1 GBd symbol rate in a superheterodyne transceiver frontend which uses an intermediate frequency in W-band between 70-90 GHz and converts into the radio frequency range between 280 and 320 GHz using an electronically generated local oscillator. As a result, it is found that a transfer gain compression of 5 dB results in an input-to-output related EVM degradation of 7 dB.