RF Circulators are ferromagnetic passive RF components that are used to provide isolation between the forward and reverse signals at the point of the signal chain where the RF circulator is placed. In some instances, an RF Circulator is also referred to as an RF Duplexer, which is not the same as an RF Diplexer. RF Circulators are commonly used at an antenna port to isolate the transmit and receive signal paths of telecommunication and sensing transceivers. An example of this is the use of a circulator at the antenna port of a radar, where the high transmit power levels could potentially damage or desense the sensitive receiver input without adequate isolation. In these types of applications, circulators are used instead of switches or diplexers/multiplexers as a circulator allows for continuous signal in both the transmit and receive signal paths simultaneously and at the same or similar frequencies without the need for time or frequency division.
Key RF Circulator Electrical Specification Parameters
Frequency Range [hertz]
Impedance [Ohms]
Insertion Loss [dB]
Isolation [dB]
VSWR
Forward input power maximum continuous wave and/or peak [dB]
Reverse input power maximum continuous wave and/or peak [dB]
Interface type, typically coaxial connectorized packaging, waveguide, or drop-in planar transmission line types
RF Circulators are three port devices that are intrinsically non-reciprocal. A typical three-port RF Circulator will allow for a signal input into one of the ports to be transferred to the adjacent port. RF energy incident on port 1 of an RF circulator will be transferred to port 2, energy at port 2 will be transferred to port 3, and energy at port 3 will be transferred to port 1. The nature of an RF circulator is that there is also isolation between the adjacent ports in the reverse direction. Hence, a signal present at port three will be present with minimal internal losses at port 1, but heavily attenuator at port 2. Keep in mind that this is the typical designation for a clockwise (CW) circulator designation and a circulator can also be designated as counterclockwise (CCW) where the circulator behavior is the opposite of what has been described.
An RF Isolator is merely an RF Circulator with a port that is terminated which provides isolation from signal energy traveling in the opposite direction of the desired orientation.