In this paper, a novel method for the extraction of aspect-independent parameters (that are analogous to complex natural resonances) of chipless radio frequency (RF) identification (RFID) tags is presented. This method is based on short-time Fourier transform (STFT). The concept is proved by utilizing classical depolarizing tags. Owing to the proposed spectrogram approach, the reading success rate of chipless RFID tag is improved by accurate extraction of identification (ID) based on the extraction of quality factors. With single tag measurement (i.e., without empty measurement) in a practical environment, the performance of the proposed spectrogram method is characterized: 1) at various misalignments of the reader and the tag. 2) at various distances for the tag mounted on numerous objects. 3) at various displacements within 3D zone of reader interrogation. The proposed technique is computationally fast due to the inherent nature of fast Fourier transform (FFT) based STFT