Compact rectangular-cylindrical cavity for rubidium frequency standard

A novel compact rectangular-cylindrical dielectric-filled 6.8-GHz microwave cavity which incorporates a step-recovery-diode (SRD) multiplier for use in a rubidium vapor cell frequency standard is discussed. The design comprises an upper rectangular part with a dielectric slab and a semi-cylindrical lower part. The cavity operates in a pseudo-TE₁₀₁ mode where the field in the upper part is compressed due to the dielectric slab and the field in the lower part is compressed due to the cylindrical shape, thus compensating for the influence of the glass cells. This increases the field intensity inside the vapor cell and at the same time retains the field uniformity. An even higher efficiency use of the magnetic field is achieved due to a high filling factor of cavity´s free space with the glass cells. The actual required input RF power is about 0.1 W, which is the known threshold value for the SRD