Waveform diversity refers to the use of various waveforms in both transmitter and receiver design to improve overall system performance. The target/channel, noise, and clutter characteristics will play a major role in future transmitter and receiver designs, in order to enhance the corresponding desired final output (target), while providing for a good disturbance (clutter + noise) suppression. In this context, the receiver output Signal to Interference plus Noise Ratio (SINR) may be taken as an optimization goal. In this paper, it is shown that this optimization procedure leads to an energy threshold on transmit waveforms, which means that for a given bandwidth, the energy of the optimum transmit waveform must exceed a certain minimum threshold value. Thus, to achieve the optimum transmit waveform for a given target, clutter and noise spectra, it becomes necessary to transmit a minimum energy below which it will not be possible to realize the maximum SINR using any waveform.