The VARACTOR, or VARICAP is a diode that behaves like a variable capacitor, with the PN junction functioning like the dielectric and plates of a common capacitor.  Varactor diodes are preferred in those location in RF circuits where band shifting or frequency variation is needed. The voltage control can be done easily by micro controllers or by a simple electronic circuitry. In the highly integrated RF circuits Varactors offer a simple and easy solution. Among others, these Varactor diodes offer some advantages. They can be assembled in a small transistor type package, they are very low cost and offer relative ease of construction on a circuit board.