Routing on the same layer as the module give a nice microstrip to the antenna. The width of the routing should give 50 ohm impedance. Parameter like PCB layer thickness, trace thickness and electrical permittivity(ε) of PCB.
The width can be calculated with microstrip impedance calculators online.
Example: https://www.eeweb.com/toolbox/microstrip-impedance

Last Update: August 8, 2017