Which device is commonly used to prevent mutual interference between two transmitters in close proximity?

• A. Low-pass filter
• B. Antenna tuner
• C. Band-pass filter
• D. Circulator

Answer: (D)

Circulators are three-port, nonreciprocal RF components that route signals in a fixed sequence. When one transmitter drives the input port, the energy is directed toward the antenna, while signals coming from the antenna or from the other transmitter are steered to the third port, not back into the first transmitter. This creates isolation between the two transmitters that are close together, preventing their outputs from interfering with each other. Low-pass or band-pass filters shape spectrum but don’t stop two active transmitters from coupling into one another, and an antenna tuner only matches impedance, not isolate transmitters. So the circulator is the device used to prevent mutual interference between two transmitters in close proximity.