Symmetrical Microstrip Lowpass Filter using Coupled Resonator

A compact microstrip lowpass filter (LPF) with excellent suppression level in stopband area using coupled resonators is presented. By connecting rectangular stubs to coupled resonators, a wide stopband is achieved. The cut-off frequency of this filter is located at about 2.9 GHz. The return loss in passband is 15.35 dB. The spurious harmonics in stopband range is attenuated from 4.19 up to 18.18 GHz under -40 dB level. The total dimensions of designed circuit are 15.16 × 8.43 mm2. With these features, the proposed LPF is appropriate for wireless networks.