An improved Group-delay approach to the tuning of coupled-resonators fiilter

An improved group delay method for the tuning of microwave filters is introduced. This method is based on the group-delay values of reflection coefficients. Measuring the group delay of reflection coefficients synthesizes all the couplings and resonant frequencies. This method requires successive trials to achieve synchronous tuning of n/2 (n=the degree of the filter, if n is odd, the tuned number will be (n+1)/2) resonators to the same resonant frequency instead of traditional (n-1) resonators. The tuning technique has been tested successfully with direct coupled six-resonators filter.