In the study of deterministic sea waves, the predictable zone refers to the area where the phase-resolvable wave field can be fully reconstructed and accurately predicted based on measured data. Under certain marine environmental and radar measurement parameter conditions, expanding the predictable zone is of great significance for domains such as quiescent period prediction (QPP) for ships and optimizing wave energy harvesting. Prior research on the predictable zone mostly relied on either temporal or spatial measurements, significantly constraining the range of the predictable zone. In this article, based on coherent microwave radar, we present a novel method combining spatial and temporal measurements to expand the predictable zone. First, the boundary of the predictable zone under a single spatial measurement and multiple spatial measurements (spatial-temporal measurement) is analyzed, and the closed-form expressions for the predictable zone are derived for both the unidirectional and multidirectional wave fields. The quantitative relationship between the predicted time at the desired spatial location and the radar parameters and wave spectra is obtained. Subsequently, the theoretical analysis of the predictable zone is validated using the numerical simulation by comparing the theoretically predictable zone with the error distributions for the unidirectional and multidirectional wavefield cases. Finally, the analysis of experimental data from Weihai, China, in 2021 also indicates that the joint spatial-temporal measurements can effectively expand the predictable zone.