  Filtering modules are essential devices of modern microwave systems given
their capability to improve the signal-to-noise ratio of the received signal or
to eliminate the unwanted interferences. For discriminating between different
components, a filter exhibits a frequency-selective response that, however, is
not able to distinguish between different signals whose spectrum falls within
the passband of the filter itself. In this regard, some electromagnetic
structures exhibiting, at the same frequency, different responses depending on
the waveform of the incoming waves have been recently proposed. In this
communication, we extend the aforementioned approach to the case of a standard
waveguide filtering module. In particular, by loading a bandpass filtering iris
with a proper lumped-element circuit, we design a waveguide component able to
distinguish between different pulsed waves, even at the same frequency,
depending on their pulsewidth. Moreover, by using this filter for capping an
open-ended rectangular waveguide, a radiating element with both frequency- and
time-domain selectivity properties is presented. The structures discussed in
this communication may pave the way to a new class of microwave systems that,
being both frequency selective and time selective, are less sensitive to noise
and interferences.
