Active circulator

Other (external) circuitry connects to the circulator ports via transmission lines.

One early technology is the use of transistors as the active devices to perform the non-reciprocal function.

[1] Varactor circuits are another technology, relying on a time-varying transmission line structure, driven by a separate pump signal.

[3] Another design approach relies on staggered commutation and integrated circuit techniques.

System designers must weigh these factors with the disadvantages of active circulators: they require DC power and sometimes a separate pump or clock signal, they can be nonlinear, and can introduce significant noise into the signal path.