A symmetric frequency multiplier includes four non-linear devices configured to receive an input signal having a fundamental mode and to provide an output having one or more harmonics; and three collinear transmission lines, each having a length of about one quarter of an input wavelength, configured to receive the outputs of the non-linear devices and configured to combine bifurcated components of the signals from the non-linear devices into two frequency-multiplied output signals. Two of the signals from the non-linear devices are provided at respective ends of the collinear transmission lines and two of the signals from the non-linear devices are provided between transmission lines, such that each of the bifurcated components of a given signal passes through a different subset of the transmission lines.