The concept of time-modulated antennas has recently been demonstrated as a means of overcoming many of the limitations currently restricting advances in the antenna art. Of special importance is the mathematical possibility of generating a pattern complex capable of providing simultaneous scan operation. This characteristic is realized by periodic time modulation of the aperture distribution. This paper discusses the theory of simultaneous "scanning" using time modulation techniques and shows that the required pattern complex is generated by a progressive-pulse aperture excitation. The fundamental equations and relationships concerning the form of pulse excitation and "scanning" coverage are derived. In addition, practical methods of physically generating the proper pulse-excited aperture are described, and the necessary detection requirements are delineated.