This paper presents the implementation and performance evaluation of a coordinated antiislanding protection for systems with multiple distributed generation units (DGUs). The proposed coordinated antiislanding protection is structured to process the d - q-axis components of the instantaneous three phase apparent powers (s(d) and s(q)) determined at the point-of-common-coupling for each DGU. The processing of sd and sq, for each DGU, is carried out by the wavelet packet transform (WPT) in order to extract their low- and high-frequency subband contents. The contents of WPT low- and high-frequency subbands offer signature information that can facilitate detecting the islanding condition and identifying the islanded DGU(s). The coordinated antiislanding protection is implemented in real time for experimental testing on a laboratory collector system that has three different DGUs. Experimental results reveal fast and accurate responses to islanding events, accurate identification of islanded DGUs, and negligible sensitivity to the type or ratings of protected DGUs. In addition, test results show that the d - q WPT-based coordinated antiislanding protection can accurately distinguish between islanding and non-islanding events, including faults, step changes in power delivery to the grid, unintentional loss of grid connection, low-voltage ride through, and sudden harmonic distortion on the grid side.