Abstract
Two properties are presented that constrain the cross-terms of Cohen-class time-frequency representations (TFRs) to appear only at signal frequencies, and only when the signal is nonzero. These properties thus guarantee strong finite support, i.e. the TFR is zero everywhere the signal or its spectrum is zero. When combined with cross-term attenuation, one can obtain TFRs with spectrogram-like interference suppression, but without the inherent time-frequency resolution tradeoff of the spectrogram.<>