lenght of a 2,4GHz trace

orange wrote:
> But what about the lenght of the trace?

It depends ...

Im many cases the length and the impedance of transmission line is used 
to match the complex impedance of the antenna to the impedance of the 
transmitter or receiver.
Although there are some electronic design programs to do this complex 
work, it can as well be done manually with a graphic method called the 
Smith-Chart.

But there are a few special cases which can make things easy if they 
apply:

1. If the impedance of the antenna is real (e.g. 50 Ohm and VSWR approx 
1.0) and if it also matches the impedance of the transmission line 
(microstrip in many cases), then the length of the line does not matter.
Of course the longer the line is the higher the attenution will be.

2. If the length of the line is lambda/2 then the impedance at the input 
and the output oft the T.L. are equal i.e. Zin=Zout.
Regardless of  the impedance of the T.L.
This means that you can either connect the antenna directly to the 
transmitter or via al lambda/2 line with arbitrary impedance.