This paper presents a new methodology to extract spectral information of radiated THz signals to enable a fully integrated broadband THz spectroscope in silicon. A classical down-conversion spectrum analysis architecture requires onchip generation of LO signals covering GHz-THz frequencies to analyze an incident spectrum covering that range. This paper presents a method to exploit the interaction between the front-end antenna and the incident signal to extract spectral information eliminating the need for extremely wideband LO generation and the entire receiver architecture following the antenna. The central premise is that the incident THz signal excites a spectrumdependent current distribution on the antenna surface and this work presents a method to measure and then estimate the incident spectrum from the impressed current distribution on an onchip antenna. The chip is implemented in 0.13 μm SiGe BiCMOS technology and measures 2.6 mm x 1.9 mm. Measurement results are presented for various incident spectra between 40.330 GHz. In addition, the paper presents a method for extracting timedomain information by exploiting the variable nonlinearities of the integrated detectors. By modifying a classical single-port antenna into a 2D multi-port scatterer, the paper presents a synthesizer-free THz spectroscope which consists of an integrated scatterer and multitude of low-power sensors capable of subwavelength measurement of near-field interactions which are exploited for spectral estimation.