How to find the norm of an imaginary exponential expresion?

I need to find the norm of the following expression

$$
|1+e^{-i2pi w}+e^{-i4pi w}|^2$$

With w real number.

For doing this I coded:

a = 1 + Exp[-2*Pi* I w] + 0.5 Exp[-4 Pi w I]
Norm[a]^2

The output is:

Norm[1 + E^(-2 I [Pi] w) + 0.5 E^(-4 I [Pi] w)]^2

So the code is not calculating effectively the norm.

a = 1 + Exp[-2*Pi* I w] + 0.5 Exp[-4 Pi w I];
Rationalize[ComplexExpand@Abs[a] // FullSimplify]^2