Abstract: A pre-characterised high frequency signal (14) is provided by means of a non-linear circuit, for example an amplifier circuit (10), fed with a first signal (12) with a component at a first, fundamental, frequency (FO). The amplifier circuit generates an output signal comprising harmonic components (14h1, 14h2, 14h3) having stable and predetermined phase relation relative to each other. Information concerning the phase relation of the harmonic frequency components is provided, for example by means of a data file (16). At least two of the harmonic components are at the tenth or lower harmonic frequencies. The signal strength of such low-order harmonic components may be relative high, thus enabling the provision of a pre-characterised high frequency multi-tone signal from the amplifier circuit with high signal to noise ratio.

Abstract: An impedance synthesis method for fundamental and harmonic frequencies using multi section tuners, because of the huge amount of possible tuning permutations, employs a search strategy based on the minimization of an ERROR FUNCTION (EF), in two steps: in a first step a coarse calibration grid is generated and the raw area is found which allows an approximate solution to the tuning task at the fundamental frequency; then a fine impedance grid is generated around the first solution using calibrated and interpolated points at all harmonic frequencies; a second search step, using the same EF, then allows fine tuning. Among the several, numerically found solutions, the most reliable one is selected based on a sensitivity criterion, which calculates the impedance change for a possible small error in repeatability of each tuning element and selects the one with the lowest sensitivity to element setting errors.