Amplitude and phase imbalance (IQ imbalance) seriously degrades the performance of FMCW radar systems with quadrature demodulator. The non-ideality of the radar signals has two main effects: The single-channel IQ imbalance leads to an image peak in the FMCW spectrum, resulting in wrong detections. The IQ imbalance between channels affects the direction-of-arrival (DOA) estimation, as the array manifold deviates from the ideal model. In the past different approaches for IQ calibration were proposed. However, existing approaches of communication applications consider the single-channel IQ imbalance only while existing radar calibration approaches consider the array imbalance only. In this work, we reformulate the single-channel IQ calibration in a radar context and propose a signal processing chain to combine single-channel and array calibration.