How to design RF PCB to ensure the 50 ohm impedance
You have to match the impedance on the transmission line. The fact that you are operating at 10-15 GHz only makes this more the case. 

Regarding the filter: you should design the filter such that it presents a 50 Ohm input impedance within your target band. Make sure your components behave up to high enough frequencies, as the self-resonance frequency of your components might make them behave very different at 5 GHz than at near-DC (your inductor might suddenly be a capacitor at a few GHz!).