Guidelines

Based on the preceding
discussion, we can give some guidelines for the loop-shaping design.

qThe loop transfer function
should be shaped in such a way that it has low gain around the frequency of
the modulus of any right-half plane zero *z*. Typically, it requires that the
crossover frequency be much smaller than the modulus of the right-half plane zero;
say, *w*c<|*z*|/2 for any real zero and *w*c <|*z*| for any complex zero with a much
larger imaginary part than the real part (see Figure 16.6).

qThe loop transfer function
should have a large gain around the frequency of the modulus of any
right-half plane pole.

qThe loop transfer function
should not have a large slope near the
crossover frequencies.

These
guidelines are consistent with the rules used in classical control theory (see Bode[1945] and
Horowitz[1963]).