Qiong Deng, Minghui Du, Peng Xu, Liang Huang, Ziren Luo

The microhertz gravitational wave (GW) band (0.1 $\mu$Hz-0.1 mHz) holds critical insights into coalescing supermassive black hole binaries (SMBHBs) and the stochastic GW background, yet remains observationally inaccessible due to technical barriers. This work presents a strategy to unlock this band by exploiting orbital resonance effects in the proposed geocentric GW antennas, circumventing the need for impractical ultralong baselines or advanced technologies. We demonstrate that when GW frequencies resonate with integer multiples of a satellite's orbital frequency (e.g., 1$\times$, 3$\times$), sustained orbital deviations amplify signals through time-cumulative effects. Benifit from orbital modulation and resonance phenomena, detector sensitivity can be enhanced by 1-2 orders of magnitude in the microhertz regime. For proposed missions like TianQin, gLISA, and GADFLI, this resonance-driven mechanism extends detectable GW frequencies and expands the observable parameter space of SMBHBs to lower masses and higher redshifts, exceeding conventional sensitivity assessments. This approach may leverage geocentric missions as cost-effective platforms to bridge the microhertz observational gap.