Compact bandpass filter with sharp passband and wide harmonic suppression using miniaturized coupled structure loaded with stepped-impedance stubs

A novel compact bandpass filter (BPF) with multiple harmonics suppression is proposed. The device uses low impedance feeding network and one-sixteenth wavelength coupled line loaded with open-ended stepped-impedance stubs. The structure generates eleven transmission zeros which enable realizing a sharp passband and wide stopband. Based on the proposed structure, two compact BPF of size around 10 mmx 20 mm on RT6010 substrate were designed, built, and tested. The two designs have fractional bandwidths of 32% (centered at 2.45 GHz) and 23% (centered at 2.8 GHz) with wide stopband extending from 3 GHz to more than 11 GHz with more than 15 dB of attenuation. (c) 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2505-2508, 2016