This article presents a novel approach to extract the coupling matrix CM of a lossy cross-coupled resonator bandpass filter with source-load coupling using admittance parameters also known as Y-parameters. The Y-parameters are calculated by characteristic polynomials corresponding to the measured S-parameters. The unloaded quality factor of resonators and the CM can be extracted from the Y-parameters. The method allows one to diagnose a filter with source-load coupling without necessity of dealing with the degenerate poles problem of the Y-parameters and the measurement noise. The proposed diagnosis method can be used in a filter tuning and speeds up its physical realization. The method is verified by a fabricated fourth-order bandpass filter and a simulated substrate integrated waveguide dual-mode filter with source-load couplings. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:713-717, 2014.