  Conventional time-modulated arrays are based on the application of
variable-width periodical rectangular pulses (easily implemented with radio
frequency switches) to the individual antenna excitations. However, a serious
bottleneck arises when the number of exploited harmonic beams increases. In
this context, the modest windowing features of the rectangular pulses produce
an inflexible and ineffective harmonic beamforming. The use of other pulses,
such as sum of weighted cosines, partially solves these issues at the expense
of introducing additional non-timing variables. We propose the discrete-time
preprocessing of rectangular pulses before being applied to the antenna to
accomplish an agile, efficient, and accurate harmonic beamforming, while
keeping the simplicity of the hardware structure.
