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
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.