A new compact microstrip dual bandpass filter using stepped impedance and λ/2 bended resonators

In this paper, a compact dual-band bandpass filter (DB-BPF) is implemented by using a pair of coupled stepped impedance resonators (SIRs) and a pair of lambda/2 bended resonators for the modern wireless communication systems such as WiMAX and WLAN (3.4 and 5.4-GHz). The physical layout is presented and explained the establishment of an LC equivalent circuit. Moreover, the second passband of the proposed dual-band bandpass filter can be independently controlled by inserting the open-circuited stubs at the end of the lambda/2 bended resonators without increasing the circuit size. Simulation results show that the second passband can be ranged from 5.6 to 4.8-GHz with the bandwidth of 400 +/- 96-MHz, whereas the first passband is fixed with the bandwidth of 280 +/- 8.5-MHz. The measured results exhibit the insertion losses (S21) lower than 1.2 and 1.4 dB, and the return losses (S11) of -23 and -32 dB at the first and second passbands, respectively, which show a good agreement with simulation results. The dual-band microstrip filter is fabricated on RT/Rogers 4003 substrate with a compact size of 0.24 lambda(g) x 0.25 lambda(g).