  The atomic-vapor cell is a vital component for Rydberg atomic microwave
sensors, and impacts on overall capability of Rydberg sensor. However, the
conventional analysis approach on effect of vapor-cell length contains two
implicit assumptions, that is, the same atomic population density and buffer
gas pressure, which make it unable to accurately capture actual response about
effect of Rydberg-atom-based sensor performance on different Rydberg atom
population. Here, utilizing a stepped cesium atomic-vapor cell with five
different dimensions at the same atomic population density and buffer gas
pressure, the height and full width at half maximum of Electromagnetically
Induced Transparency(EIT) signal, and the sensitivity of the atomic
superheterodyne sensor are comprehensively investigated at the same Rabi
frequences(saturated laser power) conditions. It is identified that EIT signal
height is proportional to the cell length, full width at half maximum and
sensitivity grow with the increment of cell length to a certain extent. Based
on the coherent integration signal theory and atomic linear expansion
coefficient method, theoretical analysis of the EIT height and sensitivity are
further investigated. The results could shed new light on the understanding and
design of ultrahigh-sensitivity Rydberg atomic microwave sensors and find
promising applications in quantum measurement, communication, and imaging.
