Aeroflex / Weinschel dc Blocks contain capacitance in-series with the center conductor to prevent the flow of dc current, while permitting RF power to flow without interruption.  These dc Blocks offer rugged construction thast includes semi-precision Type N and SMA stainless steel connectors. Molded captive inner contact/bead assembly provides controlled and stable interface dimensions.

More information here:  dc Block (dc to 20GHz)