RF, Microwave and Millimeter Wave Switch Basics in Detail by Tim Galla of Pasternack
RF, microwave and millimeter wave electromechanical relay and PIN diode switches route signals through transmission paths with a high degree of efficiency. Four fundamental RF, microwave and millimeter wave switch electrical design parameters characterize how these electromechanical relay and PIN diode switch designs perform. Several electrical parameters are associated with the performance of microwave and millimeter wave switch design for RF, but four are considered to be of fundamental importance to the RF system designer. Because of their strong interdependence, these four RF/microwave and millimeter wave switch parameters are the most important: isolation, insertion loss, switching time and power handling.
Isolation for electromechanical relay and PIN diode switches is a measure of how effectively these radio frequency switches are turned off, the attenuation between the input and output ports of the circuit. Insertion loss, or transmission loss, of an electromechanical relay or PIN diode switch is the total power lost in its “on” state. RF, Insertion loss of switches for RF, microwave and millimeter wave applications is the most critical parameter to a designer because it may add directly to the system’s noise figure. Switching time is the period a radio frequency switch needs for changing state from “on” to “off” and “off” to “on.” This period can range from several microseconds in high power RF switches to a few nanoseconds in low-power, high-speed RF switching devices. The most common definition of RF switching time is the time measured from 50% of the input control voltage (TTL) to 90% of the final RF output power. Power handling of a PIN diode or electromechanical relay switch is the maximum RF input power that the switch can withstand without any permanent degradation in electrical performance.
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