I'm designing a small board featuring a transmitter in the 900 MHz band. Since RF is definitely not my strongest subject, I'm basically trying to follow all the datasheet recomendations regarding proper layout, PCB traces, etc. However, I find puzzling the reference to an "antenna matching network" I "might" need, according to both the transceiver (AT86RF212B) and the W3113 antenna specifications.
Consider the following picture, which can be found in the antenna's reference design:
The picture above mentions said matching network, but says nothing about how to design it.
My board currently looks like this; my traces are supposed to match the antenna impedance (50 ohm), and are really short (2.6 mm. from IC pins to balun, 6.3 mm. from balun to antenna, 11 mm. total):
The component in light blue is the antenna, ZT1 is the balun and U1 is the transceiver IC. The IC output is 100 ohm balanced, while the antenna needs a 50 ohm feed.
Given this, what is exactly an antenna matching network, why should I need one and how can I design it? I've tried searching the internet about it but the references I've found were too complex or too abstract for me.