Crucial factors in power combining by oversized cylindrical cavity multiple-device structures

Power combining in oversized cylindrical cavities has hitherto not given successful results. The authors show both analytically and experimentally that the combining efficiency in such cavities can be remarkably improved by finding the optimum position and number of devices. An equivalent loss resistance, which indicates the cavity loss per device when every device generates its available power, is introduced, and the number and position of devices which minimize the quantity is obtained for a TM_0n0-mode cavity by carrying out finite-element field analysis. Power-combining experiments using TM₀₂₀- and TM₀₃₀-mode cavities confirmed the theory and achieved excellent power-combining efficiencies of, respectively, 117% and 107% in the TM₀₂₀-mode cavity with ten devices and in the TM₀₃₀-mode one with 12 devices