A Cascaded Cavity Resonator for Broadband Electric Field Enhancement in Rydberg Microwave Measurements

Rydberg atom-based microwave measurement technology has gained attention for its self-calibration, high sensitivity, and wide frequency response. To enhance sensitivity, resonators are typically employed for localized electric field enhancement. With the introduction of AC/DC Stark tuning and laser scanning techniques, resonator designs have been developed to support extended frequency coverage. However, these require sequential scanning or switching to cover the target range, limiting their applicability in passband-wide, multi-frequency detection. To address this issue, this paper proposes a cascaded cavity resonator (CCR) that enables continuous field enhancement within the target S-band range. A theoretical model was established and the key dimensions were optimized via COMSOL-based simulation of the vapor cell's spatial field distribution. Subsequently, validation through Autler-Townes (AT) effect and heterodyne technology confirms that the proposed structure enhances sensitivity by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \geq$</tex-math></inline-formula>27.2 dB within the 2.781-3.008 GHz bandwidth. This work supports systematic exploration of Rydberg-atom response across a broader spectral range and enables multi-frequency detection without stepwise tuning.