The user @TomMuc has used Uputronics SAW filter and Jetvision 3 Pole filter.
He can advise you better. He has posted some results here:
https://discussions.flightaware.com/t/the-final-filter-shootout/26821
https://discussions.flightaware.com/t/help-requested-with-outdoor-setup-with-poor-reception/27479/30