The present disclosure relates to a method for In-phase and Quadrature (l/Q) imbalance estimation and a corresponding communication apparatus. The method involves using an adaptive filter in a loopback architecture of the communication apparatus to estimate and compensate a combined TX/RX frequency-dependent l/Q imbalance. The combined TX/RX frequency-dependent l/Q imbalance is estimated by using a reference signal and two different phase shifts between a TX local oscillator (LO) signal and a RX LO signal. The resulting two estimates of the combined TX/RX frequency-dependent l/Q imbalance are used to calculate separately contributions made by a TX and a RX in the combined TX/RX frequency-dependent l/Q imbalance. By so doing, it is possible to estimate the combined TX/RX frequency- dependent l/Q imbalance without having to use additional external hardware. The calculated contributions may be then used to compensate the combined TX/RX frequency-dependent l/Q imbalance in a time domain.