Phase noise modeling and performance impact analysis in sub-THz bands

The emergence of sub-terahertz (sub-THz) communication systems demands accurate phase noise (PN) characterization in signal analyzers and frequency extension modules. This work presents a PN measurement methodology for the 110-170 GHz band using a cascaded frequency multiplication and downconversion setup. A spectrally pure intermediate frequency (IF) tone, generated by an arbitrary waveform generator (AWG), is upconverted to the sub-THz range via a ×24 frequency extension module, then downconverted using an identical module. The resulting signal is captured by a digital phosphor oscilloscope (DPO) operating up to 25 GSa/s. The PN power spectral density (PSD) is obtained from the sampled data using Welch's method and modelled with a three-pole-zero fit aligned with the IEEE 3GPP PN formulation, accurately capturing flicker and white noise regions. The measured PN is further used to assess its impact on the bit error rate (BER) of modulation schemes, including BPSK, QPSK, 16-QAM, OFDM, and OTFS. This methodology enables precise PN modelling to support the design of sub-THz communication systems with stringent noise requirements.