Why Does a Passive Antenna Show Power Gain & Why No 4x Power With In-Phase Sine Waves?

This is a very basic question that is causing me a big headache

 

1- Since a single antenna is a passive device how can it provide any power gain in a link equation? (Antenna gain in a link equation helps reducing the path loss).  Is it because it is adding vectors in phase in a certain direction just like a phase array would?

 

2-When I add 2 sine waves equal in amplitude and exactly  in phase with a Wilkinson power splitter/combiner in the lab and measure the output power with a power meter, why am I not getting 4 times the power of each of the sine waves?

I would very much appreciate an answer

Both of these questions are covered in wikipedia entries.
1) https://en.wikipedia.org/wiki/Antenna_gain

2) https://en.wikipedia.org/wiki/Wilkinson_power_divider
Look down at the references and external links.

cheers,
Richard