The performance of broadband millimeter-wave (mmWave) RF architectures, is generally determined by mathematical concepts such as the Shannon capacity. These systems have also to obey physical laws such as the conservation of energy and the propagation laws. Taking the physical and hardware limitations into account is crucial for characterizing the actual performance of mmWave systems under certain architecture such as analog beamforming. In this context, we consider a broadband frequency dependent array model that explicitly includes incremental time shifts instead of phase shifts between the individual antennas and incorporates a physically defined radiated power. As a consequence of this model, we present a novel joint approach for designing the optimal waveform and beamforming vector for analog beamforming. Our results show that, for sufficiently large array size, the achievable rate is mainly limited by the fundamental trade-off between the analog beamforming gain and signal bandwidth.