Spurious-Free Signal-Interference Dual-Band Bandpass Filters

The development of transversal signal-interference planar dual-band bandpass filters (BPFs) with extended upper stopband is addressed in this study. They are based on the exploitation of stepped-impedance-line transmission-line paths in their constituent dual-passband transversal filtering sections (TFSs) to “break” the spectral periodicity inherent to this type of filters in their traditional structures. A theoretical example of two-stage dual-band BPF derived through an optimization-based design procedure is provided to validate the approach, showing an upper-stopband bandwidth 18.1 times larger than in its classic counterpart. Moreover, a proof-of-concept prototype of this dual-band BPF design example is manufactured in microstrip technology and measured for experimental-demonstration purposes.