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 mm× 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