Attenuator Basics


                    r1           r2
          Zin o---/\/\/\---o---/\/\/\----o Zout
                           |
                           \
                           / r3
                           \
                           /
                           |
                          GND


        r3= 2*sqrt(Zin * Zout * A)/ A - 1
        r1= Zin((A+1)/(A-1)) - r3
        r2= Zout((A+1)/(A-1)) - r3

Where
        Zin (input impedance) 50ohms
        Zout(output impedance) 50ohms
        A (Attenuation, numerical ratio of input to output power) = whatever

Say you want to cut your power in half, A would be equal to .5

Plug the values into the equation and wala' you've got an attenuator.