Sharp-Rejection Wide-Band Dual-Band Bandpass Planar Filters With Broadly-Separated Passbands

This letter focuses on the application of signal-interference principles to design planar dual-band bandpass filters (BPFs) with widely-spaced broad passbands. To this aim, two classes of dual-band bandpass transversal filtering sections (TFSs) shaped by directional couplers with double loading stubs are used. Analytical equations for their transmission zeros (TZs), leading to sharp-rejection and high-selectivity performances in their filtering behavior, are given. Besides, design curves to adjust the center frequencies and bandwidths of their dual passbands are provided. Furthermore, two demonstrative microstrip dual-band BPF prototypes are manufactured and characterized.