I am moving my ADSB antennas (978mhz, 1090mhz) outside and need to purchase longer cabling using sma connectors. I prob need about 20ft for each antenna. Any particular type of cable suggested for this freq range?
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.
I got about 20 feet RG6 coax for my 1090 SDR-RTL dongle and I must say that I get a huge difference in coverage by putting an amplifier between the coax and the dongle. The dongle itself isn't that sensitive and its internal noise are probably sky high that makes it impossible to receive weak signals and that low-noise amplifier makes the dongles internal noise irrelevant.
And another vote for RG6,
Lots of adapters available and for a home-made antenna I just used an F feed-through barrel with a tincan lid for ground plane and a 1/4 wave piece of copper stuck into the barrel. Most directions I have better than 400 mile reception at commercial cruising altitudes.