What is the Reference Plane for RF Connectors


Xmultiple's Engineering Department

What is the ¡§Reference Plane¡¨?

The reference plane is simply where a Plug and a Jack meet when attached together; or in other words, where the actual RF signals within each connector stop. It is buried or embedded below the connectors end edge. The ¡§Reference Plane¡¨ is also known as the ¡§mating plane¡¨ or ¡§seating plane¡¨ or simply ¡§RP¡¨.

Why is the important? There 2 important reasons.

Mechanical: When these connectors (or adapters) are attached together, the dimension from a mounting end or reference center line to the ¡§Reference Plane¡¨ can simply be added together to determine the overall dimension engaged. As a Male Plug overlaps the Female Jack when attached, you can not determine when they ¡§mate¡¨ unless you know where the ¡§Reference Plane¡¨ is to stop the engagement. Since the ¡§Reference Plane¡¨ point is buried below the outer end, it can not be seen from a side view, and therefore must be dimensioned to a hidden line within the connector (see other attached vendor drawings for examples). This is critical when adapters are mated to each other or other mechanical parts with SMA connectors to determine where the center lines are.

Electrical: Length is critical at microwave frequencies to determine overall RF circuit performance. The ¡§Reference Plane¡¨ is used for just what it¡¦s called, a dimensional ¡§reference point¡¨ to determine RF length where one connector ends and another starts. These points must be known to determine the overall length of a RF path through a series of connectors, cable, etc.

I have also attached a marked up XM datasheet of one of the connectors we¡¦ve been discussing as a specific example. Manufacturing should know this dimension from the engineering drawings to build the connector. Unfortunately not all vendors include this dimension on typical ¡§customer drawings¡¨, however, it certain applications (which includes many I work on) it must be determined to allow the adapters to interconnect and mate with modules, adapters and/or other connectors mounted to a PC board.

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