Miniaturized Dual-wideband Bandpass Filter Using Coupled Slotted Open Stubs

This paper presents the design of a super-compact dual-wideband bandpass filter (BPF) using quarter-wavelength slotted open-circuited stubs (SOSs). These slotted open stubs are used to define the second and the third stopbands at 3 and 9 GHz respectively. Both stubs are separated by quarter-wavelength impedance transformers. Unlike conventional quarter-wavelength impedance transformers, this filter has a high-pass meandered line that is shorted to ground to form an additional stopband at zero frequency. Using this approach, a dual-wideband bandpass filter is designed, fabricated and measured. The measured results show that the fabricated dual-wideband BPF has two passbands with a fractional bandwidth of 117% and 36%, at respective center frequencies of 1 GHz and 6.65 GHz. The filter has a compact size (0.09 lambda g x 0.05 lambda g) and exhibits an attenuation level greater than 20 dB up to 12 GHz.