Abstract: The zero-IF architecture has been widely used in recent years, but inphase/quadrature (I/Q) imbalance deteriorates the quality of received signals seriously. Eliminating I/Q imbalance through back-end compensation algorithms is one of the most efficient methods, but the existing literature does not comprehensively study the time mismatch (TM) error in broadband I/Q imbalance. An augmented error model of wideband I/Q imbalance including TM errors is established in this paper. The data-aided method is used to estimate the imbalance value in this paper, and then the polynomial fitting is applied to decompose the phase mismatch. Based on the decomposed error, a corresponding compensation structure based on a real-valued finite impulse response (FIR) filter with nonlinear phase is proposed to eliminate the separated imbalance errors. The design of the compensation filter firstly selects the optimal delay value according to the theory of least square (LS) to ensure the causality, and then utilizes the conjugate gradient square (CGS) algorithm based on the Krylov subspace, incorporating the design idea of increasing the transition band frequency interval to design the compensation filter. The experimental results show that the designed compensation filter improves the compensation accuracy of the imbalance error under the premise of ensuring the attenuation characteristics of the transition band, and the system with I/Q augmented imbalance can obtain a nearly 77 dB relative image ratio (RIR) improvement after introducing the compensation structure designed in this paper.