Toward Multi-Service Atomic Receivers: Co-Referenced, Co-Located Detection of Sub-MHz and Microwave Signals

Space-Air-Ground Integrated Networks (SAGINs) require sensing infrastructures covering sub-MHz to microwave frequencies. While Rydberg sensors offer ultra-wideband capabilities, a unified framework for concurrent detection remains unexplored. This paper proposes a unified atomic receiver simultaneously recovering microwave waveforms via LO-assisted mixing and sub-MHz fields via bias-assisted Stark modulation. We develop a linearized equivalent baseband model that transforms stiff time-domain dynamics into a rapid frequency-domain solution. Our analysis reveals a fundamental trade-off: the strong LO field required for microwave mixing induces Autler-Townes broadening, suppressing the spectral slope essential for lowfrequency detection. Consequently, we formulate a systematic strategy to reconfigure the receiver for microwave-priority, low-frequency-priority, or balanced sensing. By unifying disparate modalities within a single quantum aperture, this work offers a vital solution to reduce hardware complexity for size-constrained integrated sensing and communications platforms.