As you go up in frequency, the type of coax you use becomes more important. If you scrimp on coax, then often you need a pre-amp to offset the attenuation. At a certain point, coax doesn't work very well anymore, and you have to go to waveguide.
Just before you get to waveguide, there's a class of coax called heliax. This is a very stiff coax that comes in various sizes (1/2", 7/8"). The 1090 MHz band has traditionally used heliax (even in commercial radar/IFF systems). Some use heliax with nitrogen in it to handle higher power.
So, my recommendation would be to skip the pre-amp, unless it had a noise-figure of less than 1 dB (the higher the noise-figure, the more noise it amplifies), use 1/2" heliax down from the antenna to the radio room, and then a short piece of flexible coax to the radio. No pre-amp.
This high-lights how these radios are actually poor designs. There is no reason you need to transport microwave signals long distances. If the 1090 MHz receiver was at the antenna, you could then just send a video signal down to the radio room. Video doesn't require fancy coax. If I was to design a new radio for base-station use, I would design the digital side of the radio to sit on a 1X PCI-E circuit card, and have a remote analog side at the antenna. This then gets rid of the ethernet and USB interface. Plugging things into the computer buss has always been better than the I/O interface.
I own a first version of the SBS-1. This circuit board was designed so you could cut-off the analog side of the board, move it to the antenna, and use cheap coax. That's how I've run mine. Rather than run power up the coax to power-up the remote receiver, I used a solar panel that has a built-in battery. This provides 5 volts DC to the receiver, and the battery can run for days without sun. It's very green! They sell these solar panels at the home and garden center for use with lawn lights that have LED's in them. Very cheap.
Pre-amps are to radio, what cardboard box homes are to humans.
