We consider the problem of designing transmit waveforms based on target signature exploitation for detection of weapons under single-antenna monostatic radar operation. The target impulse response changes with the target orientation relative to the radar, which may not always be available or accurately determined in practical situations. We assume that the true target impulse response belongs to some uncertainty class of impulse response functions, which encompasses the impulse responses corresponding to the various target orientations. A transmit waveform-receiver filter combination is then designed to achieve the best lower bound on performance within this class, assessed by signal-to-clutter-and-noise ratio. Supporting design examples using electromagnetic modeled data are provided.