Before revision: A third parameter is set by choosing a resonant frequency, this is set to (at least) the maximum frequency the network is required to operate at.
After revision: Equivalently, every transmission pole, sp in the s-domain left half-plane must have a matching zero, sz in the right halr-plane such that sp=−sz.ChaloupkaS. Kolesov, p. 233A third parameter is set by choosing a resonant frequency, this is set to (at least) the maximum frequency the network is required to operate at.