MMA25312BT1 the output resistance ?

[danusha]

The datasheet uses a microstrip line to match the output resistance, but it is not specified what the output resistance of the amplifier itself has.
To calculate the matching , I need to know the output resistance .

[ErikaC]

Hello,

Microstrips are parts of the impedance matching network, typically 50 ohms. 

But you can also refer to Microstrip Design Techniques for UHF Amplifiers.

Hope it helps.

Regards.