  Electromagnetically induced transparency (EIT) in atomic systems involving
Rydberg states is known to be a sensitive probe of incident microwave (MW)
fields, in particular those resonant with Rydberg-to-Rydberg transitions. Here
we propose an intelligible analytical model of Rydberg atomic receiver's
response to amplitude- (AM) and frequency-modulated (FM) signals, and compare
it with experimental results: we present a setup that allows sending signals
with either AM or FM and evaluating their efficiency with demodulation.
Additionally, the setup reveals a new detection configuration, using all
circular polarizations for optical fields and allowing detection of circularly
polarized MW field, propagating colinearly with optical beams. In our
measurements we systematically present that several parameters exhibit local
optimum characteristics and then estimate these optimal parameters and working
ranges, addressing the need to devise a robust Rydberg MW sensor and its
operational protocol.
