A UNIFIED APPROACH TO THE DESIGN, MEASUREMENT, AND TUNING OF COUPLED-RESONATOR FILTERS

The concept of coupling coefficients has been a very useful one in the design of small-to-moderate bandwidth microwave filters, It is shown in this paper that the group delay of the input reflection coefficient s of sequentially tuned resonators contains all the information necess ary to design and tune filters, and that the group-delay value at the center frequency of the filter can be written quite simply in terms of the low-pass prototype values, the LC elements of a bandpass structur e, and the coupling coefficients of the inverter coupled filter, This provides an easy method to measure the key elements of a filter, which is confirmed by results presented in this paper, It is also suggested that since the group delay of the reflection coefficient (i.e., the t ime taken for energy to get in and out of the coupled resonators) is e asily measured, it is a useful conceptual alternative to coupling conc epts.