Comments on “Wideband Coupled-Line Microstrip Filters With High-Impedance Short-Circuited Stubs”

In the above paper, authors analyze the realization of coupled-line filters by means of the II equivalent circuit of a short-circuited coupler. Therefore, a a wide-band bandpass filter composed of several quarter-wavelength coupled-line sections connected in cascade is designed and values for the II equivalent network are calculated. Then, an alternative to implement a high-impedance short-circuited stub (Fig. 1(a)) using a pair of coupled lines with three short circuits (Fig. 1(b)) is proposed. Nevertheless, the equation [1, (2)] used to calculate the equivalent characteristic impedance Z of the proposed alternative seems to be incorrect.