Experimental and numerical study of the microwave field distribution in a compact magnetron-type microwave cavity

The homogeneity of the microwave magnetic field distribution inside a microwave cavity resonator is of crucial importance for the performance of high-stability vapor-cell atomic clocks, in particular when operating in the pulsed regime. Here we report on measurements and numerical simulations of the microwave field distribution inside a highly compact magnetron-type microwave cavity. A microwave field imaging technique is used to measure the microwave field distribution over the cavity volume occupied by the Rb vapor cell. Over the measured volume, we find a variation in the microwave field´s z-component (relevant for the clock performance) of 20%, with good agreement between experiments and simulations. The presented results are relevant for assessing clock performance limitations arising from the cavity studied, and give design guidelines for future improved cavities of similar type.