RF circulator

A radio frequency (RF) or microwave circulator is used to pass RF signals and block returned signals. The circulator is a three-terminal device which passes signals input to one port to the next port in a rotational fashion without allowing signals to pass in the opposite rotation. Circulators generally contain a microwave circuit comprising an arrangement of conductors and ferrite blocks, and a magnetic circuit providing a magnetic biasing field applied to the ferrite blocks that act as a non-reciprocal media for propagating radio frequency signals throughout the device. RF circulators are suitable for essentially any radio frequency (RF) application, including communications. RF circulators are also useful as isolators, easily made by tying the third circulator port to ground through a resistor. RF circulators can be built in resonant structures such as radio frequency resonant cavities and in waveguide at higher frequencies. Circulators may also be realized in planar configuration using stripline or microstrip technology which employ a planar resonating element between two ground plane conductors (stripline) or coupled to a single ground plane conductor (microstrip). Radio frequency and microwave circulators employ a DC-biasing magnetic field generated in ferrite material enveloping a conductor to provide at least one non-reciprocal transmission path between signal ports on a network. In a radar or communications system it is often advantageous to couple multiple devices, such as a transmitter and a receiver, to the same antenna. A common approach uses a radio frequency circulator to isolate the transmitted signal from the received signal to avoid overloading the receiver front end. An array antenna can include a plurality of radio frequency (RF) circulators disposed in an array in a manner in which RF signals can be received from or transmitted to the same individual radiator.