What are Absorptive and Reflective Switches?

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- everything RF

Jul 22, 2019

Absorptive and Reflective terminations in RF Switches refer to the way the ports are terminated in a switch.

An Absorptive Switch (also known as a terminated switch) is a switch whose output ports are terminated with a 50 Ohm load to match the systems impedance. This way when the switch is OFF, the signal is absorbed by the termination/load at the port and not reflected back in to the switch. This results in low VSWR (voltage standing wave ratio). When the switch is turned ON, the signal propagates thru the switch and the terminated port is isolated out. This way the switch has a low VSWR in both the on state and off state.

Absorptive switches are used in applications where you need to minimize reflections back to the RF source. But they have low power handling capability, are more complex to design and cost more than non-terminated switches or reflected switches.

A Reflective Switch has no termination (load) at the output ports the switch is not active. This results in the input signal being reflected back to the source. As a result of this Reflective switches have a higher VSWR. These switches are easier to design, are lower in cost and can handle a higher amount of power compared to absorptive switches.