Optimization of a next-generation comb generator for accurate large-signal measurements on a user-defined frequency grid

In order to accurately calibrate large-signal measurement instruments at RF and microwave frequencies, periodic pulse-shaped signals are used. However, when performing modulated measurements, the repetition rate of this pulse-shaped signal has to be kept very low. As a result, it is almost impossible to measure such a signal using state-of-the-art instrumentation due to the required signal-to-noise ratio. Recently, a next-generation comb generator using Pseudo-Random Bit Sequence (PRBS) has been proposed. It allows to generate dense modulation tones around the carrier and its harmonics and to balance the power of these modulation tones and the desired modulation bandwidth. Moving it one step further, the energy can be optimized for a desired number of discrete tones using a Tone Selective Bit Sequence (TSBS) instead of a PRBS sequence. In this paper two methods are presented to realize such a TSBS using a genetic-algorithm-based global optimization. It is shown that these methods outperform the initially proposed method which is based on random phase and clipping, especially when the number of desired tones increases.