How do I decide between a waveguide solution and a coaxial solution for a given frequency and power level?

Deciding between a waveguide and a coaxial solution depends on the operating frequency, power level, insertion loss tolerance, bandwidth requirements, and physical size/weight constraints. Waveguide is preferred when: operating frequency is above approximately 18 GHz (where coaxial cable losses become prohibitive, exceeding 1-3 dB/meter), power levels exceed 100 watts CW (where coaxial cables and connectors approach their voltage breakdown and thermal limits), minimum insertion loss is critical (waveguide loss is 5-10x lower than coaxial cable at the same frequency), and phase stability is important (waveguide has better thermal phase stability than coaxial cable). Coaxial cable and connectors are preferred when: operating frequency is below approximately 18 GHz (where coaxial losses are manageable), power levels are moderate (under 100 W CW for most connectors), flexibility is needed (waveguide is rigid; coaxial cable is flexible), size and weight are constrained (coaxial is more compact than waveguide at the same frequency), and broadband operation is needed (coaxial operates from DC to its upper cutoff frequency, while waveguide operates only within its single-mode bandwidth, typically 40-67% fractional bandwidth). At intermediate frequencies (12-40 GHz), both technologies are viable and the choice depends on the specific loss, power, and size requirements.