A first amplifier is coupled to an output node via a first line having first and second portions. A second amplifier is coupled to the output node via a second line having first and second portions. An auxiliary amplifier is coupled via an auxiliary line network to a first intersection between the first and second portions of the first line, and to a second intersection between the first and second portions of the second line. For each of the first and second lines, the first and second portions have a higher-impedance portion and a lower-impedance portion whose combined length is a half wavelength. Lengths of the respective first portions of the first and second lines sum to half a wavelength, and the lengths of the respective second portions of the first and second lines sum to half a wavelength.