Power combining in coaxial waveguide by printed planar probes is investigated. Combiners are designed and implemented at 8-12 GHz and 15-18 GHz. Average introduced insertion loss is measured as 0.5 dB per branch. Power amplifier modules are designed and implemented for both bands. similar to 20 W output power at 8-12 GHz and similar to 12 W output at 15-18 GHz are achieved by efficient power combining.