Comparative Study of Two Architectures Suitable for the Generation of Wideband Signals at Sub-THz

This paper presents a comparative study of two architectures for generating wideband modulated signals at sub-THz frequencies using a frequency bonding approach, focusing on achievable output signal quality. The first architecture generates a wideband signal at an intermediate frequency (IF) and up-converts it to sub-THz frequencies using a heterodyne mixer. The second approach generates multiple narrowband signals at IF, up-converts each to sub-THz, and then combines them. The study shows that, under linear up-converter operation, both architectures achieve similar signal-to-noise ratios (SNR) and are limited by the noise floor. However, replacing the combiner in the second architecture with a frequency duplexer improves the SNR by 3 dB. At higher IF power levels, where up-converter nonlinearity becomes significant, both architectures require digital predistortion to mitigate distortion. Despite this, the second architecture demonstrates superior adjacent-channel power ratio (ACPR). D-band measurements confirm that the second architecture enhances ACPR by up to 8 dB at high IF power levels when generating a modulated signal with a carrier frequency of 142.5 GHz and a modulation bandwidth of 1.2 GHz, while performance at lower power levels remains comparable.