We evaluate the potential of a new generation microwave cavity by double resonance spectroscopic studies. Both, the cell and the microwave cavity are microfabricated. This allows a substantial size reduction for the physics package, without compromising the RF field geometry and the optical quality of the cell windows. We demonstrate short term stability of 5 × 10 -12τ-1/2 (1-100 s), and below 1 × 10 -12 up to 103 s. Finally, we report on the AC stark shift effect, one of the main limiting factors for long term clock stabilities. © 2013 IEEE.