Base Plate Temperature For Ferrite Isolator/Circulators

By Cobham Sensor Systems

Introduction
This application note defines "baseplate temperature" for M/A-COM's circulator/isolator product lines. The choice for base-plate materials and their impact on the power handling capability are also discussed.

Chip resistor and base plate
High power chip resistors are commonly used in stripline-junction ferrite isolators as isolated-port terminations. Some circulators also utilize chip attenuators at the isolated port. The main function for such terminations/attenuators is to dissipate the reflected RF power in the event of gross mismatch at the output port thus protecting other parts in the system. The chip suppliers typically specify the power handling capabilities of the chips with the criterion that the base-plate is kept below a certain temperature. Otherwise a de-rating factor must be used.

"Base plate" is usually defined (by the chip manufacturers) as the heat-sink that directly attaches to the chips, i.e. right underneath the chip (see [1] for an example). This may be different from where M/A-COM's customers monitor/maintain the system temperatures. M/A-COM's defines the "base-plate temperature" to be that of the area on the bottom side of the housing assembly beneath the high power termination/ attenuator. In most cases, close approximation of this temperature can be obtained by observing the area next to the chip.

Downloads:
•Application Note: Base Plate Temperature For Ferrite Isolator/Circulators