Frequency Response of Strip-line Traveling-Wave Directional Filters (Correspondence)

Coale analyzed the single resonator strip-line traveling-wave filter shown in Fig. 1 by a perturbation method. Design criteria were formulated relating loaded Q to pertinent circuit parameters. Experimentally it is observed that properly aligned filters exhibit a frequency response which is approximately Butterworth. The purpose of this communication is to show that the approximate frequency response of narrow band-width filters in the absence of dissipation and resonator discontinuities is theoretically Butterworth. Comments on the design problem are included as well as a discussion of the effects of resonator discontinuities.