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A dc block is usually nothing more than a capacitor that has low series reactance at the RF frequency, and allows you to separate dc voltages along a transmission line. A parallel coupled line can also serve as a dc block.
DC blocks can be placed in the "hot" conductor of a transmission line such as coax, or the ground plane, or both, as shown below. Many vendors offer coaxial dc blocks in all three arrangements. When would you want a dc block in the ground plane? Perhaps you want to inject a voltage onto the source of a shunt FET, which is grounded to your fixture. Users of this type of dc block must be aware that their equipment could provide a voltage when they touch it. Careful where you drop that wrench!
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Three types of dc blocks
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