Features of Frequency Response Transformations of RLC Circuits into Opposite Response when Using them as a Load of Coupled Strip Lines with Unequal Waves Phase Velocities

The frequency characteristics of coupled strip lines (CSL) sections, with RLC band-stop filters (BSF) included in the diagonal arms, have been considered. The variable parameter of CSL was the phase velocities ratio of inphase and antiphase excitation modes of waves propagating in the lines. The scattering matrix coefficients and group delay time have been calculated for inphase and antiphase waves velocity ratios of 0.8, 1.54, 1. 02.It has been shown that the sections have the property of band-pass filters (BPF) with the following features. First, at an average frequency of 1 GHz of the passband at out-of-band frequencies up to 8 GHz there are no stray band-passes with relatively low return loss at the specified phase velocity ratios. Second, there is an optimal value of the phase velocity ratio close to 1.0, at which the insertion loss and return loss are minimal. Third, the considered links of CSL give a maximum group delay time with an increase up to 3 ns at the center frequency of the passband in contrast to the classical links of bandpass filters on coupled lines. It has been shown experimentally that the possibility of using sections loaded with band-stop RLC-filters as links of band-pass filters with minimal losses of less than 2 dB and with the properties of absorption-type filters at out-of-band frequencies in the absence of stray passbands.