  The Simons Observatory (SO) is an upcoming polarization-sensitive Cosmic
Microwave Background (CMB) experiment on the Cerro Toco Plateau (Chile) with
large overlap with other optical and infrared surveys (e.g., DESI, LSST, HSC).
To enable the readout of \bigO(10,000) detectors in each of the four telescopes
of SO, we will employ the microwave SQUID multiplexing technology. With a
targeted multiplexing factor of \bigO{(1,000)}, microwave SQUID multiplexing
has never been deployed on the scale needed for SO. Here we present the design
of the cryogenic coaxial cable and RF component chain that connects room
temperature readout electronics to superconducting resonators that are coupled
to Transition Edge Sensor bolometers operating at sub-Kelvin temperatures. We
describe design considerations including cryogenic RF component selection,
system linearity, noise, and thermal power dissipation.
