A Notch Filter Design and Realization using Cross-coupled Line Structure

This paper presents a notch filter with coupled line structure. The filter works at a center frequency of 3 GHz for S-Band applications. A good rejection filter, narrow bandwidth, and compact filter are needed to improve the performance of a notch filter. The proposed notch filter comprises four coupled lines arranged like a cross-coupled. Based on the even-mode and odd-mode characteristic impedance of the parallel-coupled line filter, the dimensions of coupled lines were calculated. An electromagnetic software simulation was used to investigate and optimize the design. In this structure, the other coupling in the center of the structure occurred. Two kinds of bends in the center of the structure were applied to acquire the performance based on the specification. From the simulation results, all the bends showed a good performance. The fabrication and measurement of the notch filter on RT/duroid 5880 as a substrate were done to validate the proposed design. The fabricated notch filter has a size of 50 mm x 50 mm. As a result, the input reflection coefficient (S11) and insertion loss (S21) at working frequency have good agreement with the specification. The difference is in the bandwidth, where the bandwidth is reduced by 15 % from the required specification, which may be caused by the fabrication process.