In this paper, we study an additional spatial diversity mechanism added to a cavity-backed frequency-diverse aperture for computational imaging applications at X-band frequencies. It is shown that the dynamic variation of cavity modes achieved by means of a simple, multi-port excitation mechanism can significantly simplify the diversity constraints on the frequency-diversity technique for computational imaging and can substantially improve the fidelity of the reconstructed microwave images. Leveraging the proposed technique, we present that, for the selected number of measurement modes, the condition number of the studied computational imaging problem is improved by 8.5 times in comparison to using the frequency-diversity as the only diversity mechanism. The reconstructed X-band images of various targets, including the letters “Q”, “U” and “B” reflect on this improvement and exhibit a higher reconstruction quality, significantly assisting in the identification of the imaged objects. We also present that the resolution limits of the frequency-diverse computational imaging system synthesized using the proposed multi-port cavity are in excellent agreement with the theoretical resolution limits.