In this paper, a wideband coaxial power combiner with tray con guration, employing twenty 1-Watt elements mounted on antipodal nline boards, is implemented to achieve a rather high power microwave ampli er in the frequency band of 6-18 GHz. The average gain, Continuous Wave (CW) output power and Power-Added E ciency (PAE) of the combiner are measured as 17 dB, 15 Watts and 17%, respectively with ripples of less than 3 dB. In order to investigate the combining e ciency, the passive structure is fabricated and tested in the rst step. Its main components, i.e. the coaxial adapter and the antipodal nline boards, are synthesized by using Klopfenstein's optimum impedance taper, and simulated by Ansoft HFSS. Next, the active devices are added to the system. Stability, thermal management and life time issues are examined and addressed in this step. The system reliability is also demonstrated as graceful degradation due to the failure of devices.