Implementation of Compact UWB Bandpass Filter With a Notch-Band

An ultra-wideband (UWB) bandpass filter on microstrip line with notch-band, compact-size and improved upper-stopband performances is presented and implemented. A modified non-uniform resonator is at first formed by transversely attaching three pairs of impedance-stepped stubs. Its resonance behavior is thoroughly characterized so as to allocate the first three resonant frequencies within 3.1-10.6 GHz band while suppressing spurious harmonics in the upper-band. As this resonator is linked at two sides with two feed lines via interdigital coupled lines with enhanced coupling degree, a preferred UWB passband is realized. Then, one of two arms in the coupled-line sections is largely extended and folded, aiming to create a notch band at the frequency of 5.6 GHz by virtue of out-of-phase transmission cancellation. Two filter prototypes are optimized and fabricated to demonstrate the notch-band-included and upper-stopband-improved UWB bandpass performances.