RF isolators and RF circulators are passive devices that are used to control the propagation of RF signals. RF isolators are two-port units that allow signals to pass in one direction while providing high isolation for reflected energy in the reverse direction. RF circulators have three or more ports and are used to control the direction of signal flow in a circuit. They allow the signal entering one port to pass to an adjacent port in either a clockwise or counter-clockwise direction, but not to any other port. Three-port or Y-junction circulators are commonly available. In these devices, the signal flow is normally expressed as 1 to 2, 2 to 3, and 3 to 1. For example, when the input is port 1, the RF signal exits port 2. Ideally, port 3 remains isolated and does not receive or pass the signal. Some RF isolators and RF circulators are designed for use with a coaxial cable. Others are designed for use with a waveguide. RF isolators and RF circulators that contain magnets are not designed for mounting near ferrous materials because the close proximity of metals such as iron can change the frequency response.
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