A design of the compact microstrip bandpass filter with a wide passband and broad stopband

Abstract

A compact microstrip bandpass filter with a wide passband and broad stopband is proposed. In order to miniaturize the circuit size, the interdigital capacitor is adopted. Moreover, the open- and short-circuited coupled lines are also employed to generate the transmission zeros around the passband skirts. This bandpass filter is developed at 2.45 GHz for the central frequency. The measured bandwidth is 45% with 10-dB for the return loss. Furthermore, the stopband can be extended to 11.7 GHz (4.8ƒ0) with 27 dB for the suppression. In addition, the circuit size is 0.14λg × 0.15λg.