A coaxial cable is a wire insulated and shielded within insulators and braided wiring to prevent EM interference and to keep the cable secure. The type of cable you select plays an important part in determining your link budget.
Coaxial cables generally contain the parts shown above.
Centre Conductor: The centre conductor is generally made of pure copper, or coated with steel or aluminum, and is the part which actually conducts the RF electricity.
Dielectric: The conductor is surrounded by a dielectric material, generally PVC, polyethelyne (PE), teflon, or polypoplyne (PP). Its job is to keep the conductor in the middle of the wire, and insulate it from conduction by the braided shield. WIthout the dielectric, movement of the conductor around the cable could also result in EMI. The dielectric’s dielectric constant is an important figure and should ideally be close to 1. As an example, PVC has a dielectric constant of 3 or 4.
Foil Shield: Simple aluminum foil encasing that is sometimes found in cables to prevent against RF interference. Shielding also helps EM fields from leaking out of the wire.
Braided Shield: Braided copper wire that is able to pick up EMI to reduce noise. Generally, these have a % coverage, which can be between 30-95%.
Outer Jacket: Standard wire insulator for protection from the elements
Perhaps the most important criteria. If your impedance is not 50 ohms, immediately reject the cable. Most RF circuit design for CubeSats involves using 50 ohms everywhere. If the impedance between your cable and your connector or antenna or transceiver is not the same, some of the RF signals will bounce back and cause interference as well as a loss in transmit power.
Second most important criteria. Attenuation is a measure of the loss of signal (usually given in dB) per unit length, due to things like resistance. Attenuation is proportional to frequency, so a value is generally given for a particular frequency.
A measure of how fast an EM signal moves through a wire compared to through free space. Velocity factor gives a fraction or percentage for how fast the signal travels compared to the speed of light. Latency or signal delay is usually given in ns/m, and tells you how fast the signal takes to move through a metre of wire. Velocity factor is related to the dielectric constant of the dielectric surrounding the conductor, and is equal to 1/e, where e is the dielectric constant.
The more the layers of shielding, generally the better. The higher the coverage of shielding, the better, particularly because this protects against radiation effects in space too. Having the RFI foil shielding is also a big advantage.