Design of compact meandered dual mode wideband microstrip bandpass filter using tuning stubs

In this paper, a new compact meandered dual mode wideband microstrip bandpass filter design using tuning stubs is proposed. Proposed filter is constructed by using bandstop filter with directly connected orthogonal feed lines. The tuning stubs which are of quarter wavelength, located at the opposite sides of input and output sides create a passband within a wide stopband. Perturbation patch located at orthogonal corner with respect to the input and output feed lines excite dual degenerate modes. These dual degenerate modes are responsible for creating two transmission zeros on both upper and lower side of the passband thereby improving the selectivity of the filter. The designed filter which is simulated shows a very low insertion loss of 0.6 dB and return loss level of 11 dB at a center frequency of 4.1 GHz. The fractional bandwidth (FBW) is 49%. Proposed filter achieves a nearly 10% surface area reduction compared to the square loop operating with the same perimeter of the structure.