A new QFT design method for SISO cascaded-loop design, which is different f
rom the conventional inner-outer procedure and the outer-inner procedure, i
s proposed in this paper. The desired uncertainty of the inner loop after c
losure is prescribed as a design specification before designing the inner c
ontroller, which is done by introducing an appropriate weight function. The
inner loop design, therefore, is transferred into a sensitivity reduction
problem. Then, the outer-loop design becomes that of a plant with mired unc
ertainty which can be carried out as usual. rn this method, the weight func
tion is an important design factor, which actually allocates the control bu
rden between the inner and outer controllers. This method not only removes
the arbitrariness in the closure of the inner loop in the inner-outer proce
dure, but also cart reduce the number of iterations needed, which therefore
could give a significant reduction in the outer controller bandwidth as is
demonstrated in two examples.