Compact microstrip dual-mode dual-band bandpass filter with wide stopband

A compact microstrip dual-mode dual-band bandpass filter is presented. The filter consists of two E-shaped resonators and two T-shaped feedlines. By utilising the odd-mode and even-mode resonance properties of the proposed E-shaped resonator, the new filter is designed with two transmission poles in both passbands. Furthermore, the introduced two T-shaped feedlines and a coupling between them can result in multi-transmission zeros in the stopband, which will improve the selectivity of the filter. To validate the design theory, a dual-mode dual-band filter with two passbands located at the centre frequencies of 1.8 and 2.4 GHz, respectively, were designed and fabricated. Both experimental and simulation results are provided, with good agreement.