What is the difference between circulators and isolators?

In high-frequency circuits (RF/microwave, frequency 3kHz–300GHz), Circulator and Isolator are key passive non-reciprocal devices, widely used for signal control and equipment protection.

Differences in structure and signal path

Circulator

Usually a three-port (or multi-port) device, the signal is input from only one port and output in a fixed direction (such as 1→2→3→1)

Isolator

Basically a two-port device, it can be regarded as connecting one end of a three-port circulator to a matching load to achieve unidirectional signal isolation
Only allow the signal to pass from input to output, prevent the reverse signal from returning, and protect the source device.

Parameter and performance comparison

Number of ports: 3 ports for circulators, 2 ports for isolators

Signal direction: circulators are circulated; isolators are unidirectional

Isolation performance: isolators usually have higher isolation and focus on blocking reverse signals

Application structure: circulators have more complex structures and higher costs, isolators are more compact and more practical

Application scenarios

Circulator: Applied to radar, antennas, satellite communications and other scenarios to achieve functions such as transmit/receive separation and signal switching.

Isolator: Commonly used in power amplifiers, oscillators, test platforms, etc. to protect equipment from damage by reflected signals.