Design of a microwave multisine source using allpass functions estimated in the Richards domain

In this paper a low-crest-factor microwave multisine source is developed. This is a broadband, periodic signal with a low crest factor (peak factor to effective value ratio). The design method consists of generating a pulse with a broad spectrum, amplitude filtering to get the desired power spectrum, and phase filtering for lowering the crest factor. A new technique to realize microwave phase filters is described. First, the properties of a rational allpass function in the Richards variable are examined. This enables us to estimate the coefficients using a nonlinear optimization technique, The function is realized with coupled transmission line filters. Using this general technique, a microwave multisine consisting of 20 components in the band [100 MHz, 2 GHz] is realized with a crest factor of 2