Abstract: A method of classification of a device by recognizing distorted signals, generally a RF antenna pattern, emanating therefrom wherein a trainable recognition system, preferably a neural network, is provided. Known distorted signals are applied to the trainable recognition system to train the recognition system to recognize individually each of a plurality of different signals having distortion therein. Unknown distorted signals are then provided emanating from a remote device and the unknown distorted signals are then used to classify the remote device by analyzing the received unknown distorted signals in the trained recognition system. The steps of training and classifying each include the step of converting the signals from the time domain to the frequency domain. The steps of training and classifying also can each include the step of down sampling the frequency domain signals to compress the signature content.