Limitations of the describing function for limit cycle prediction

We consider comparator-based nonlinear feedback systems, and use Tsypkin's method to develop a strategy with which to rind systems with low-pass linear part for which the describing function technique erroneously predicts limit cycles. We produce an infinite set of examples of systems with very low-pass linear parts for which the describing function technique predicts spurious limit cycles, and also provide a more practical example in which limit cycles are erroneously predicted.