In this paper, the performance degradation of a MIMO OFDM-based beyond-3G system, due to various impairments in the radio frequency (RF) circuitry such as AM-AM distortion of power amplifier (PA), in-phase/quadrature-phase (IQ) mismatch effects, is investigated. In order to accurately assess the overall effects of RF impairments on the system performance, constellation diagram and power spectral density (PSD) of the waveform as well as the traditional quantitative figures of merits like error vector magnitude (EVM) of the complete baseband/RF link are used. By analyzing the experimental results, the specification for the RF impairments that ensures a tolerable level of performance can be determined