You could do worse than a good grade of RG6 quad shield. 20 ft is only going to produce 1.3 dB loss. Another factor to consider is that if you go to a much lower loss cable it will become thicker, heavier, hard to bend... and not work very well with SMA connectors. So you'll need pigtails to get from the thick heavy low-loss coax to SMA. Those pigtails introduce some loss... so what have you gained by using something other than the relatively flexible, low-loss RG6? And RG6 is what the satellite and cable TV systems use... which often operate at freqs higher than 1090. I use it on my ADS-B setup and it's fine.