UKPassats

I have recently fitted an aftermarket Android stereo into my 55 Passat, which sounds great. I was advised that I needed to fit a double fakra antenna to boost the radio signal. I purchased one of these off eBay and have fitted it but the radio reception is still bad. There is a blue lead which I have connected to the antenna lead in the iso loom but no improvement.
Has anyone out there had a similar experience and how can I make the radio reception better.
Gavin