A Bandpass Filter with Adjustable Bandwidth and Predictable Transmission Zeros

In this article, a microstrip bandpass filter with an adjustable bandwidth and predictable transmission zeros is proposed. The proposed filler is implemented by combining two hairpin edge-coupled resonators with interdigital capacitors. Compared to typical edge-coupled filters. the proposed filter provides a wider band-width resulting from a higher coupling strength between its resonators. To further increase the coupling and consequently the bandwidth, a pair of etched slots in the ground plane is used. By adjusting the geometrical parameters of the interdigital capacitors and etched slots, the bandwidth can be easily adjusted. The filter features two transmission zeros, which are determined by means of the semi-analytical model developed as part of this work. Furthermore, the proposed filters can be cascaded to obtain it sharper cutoff frequency response. Frequency responses of the filters from measurements are in good agreement with those simulated using IE3D in the 5-9 GHz range. (C) 2009 Wiley Periodicals. Inc Int J RF and Microwave CAE 20 148-157, 2010