Bandpass filter based on asymmetric funnel shaped resonators with ultra wide upper stopband characteristics

Abstract

A novel microstrip bandpass filter with wide passband, good skirt selectivity and very good passband reflection characteristics using asymmetric funnel shaped resonators is presented in this paper. IE3D simulation software is used for the design and analysis of the proposed filter and the electric field intensities at various frequencies of interest are plotted and verified the role of even and odd mode resonances in achieving wide passband. There are six modes, including three even and three odd modes for the developed filter. Novel equations are derived for finding out the location of transmission zeros and the role of resonators in achieving sharp selectivity are verified. The out of band performance of filter is very good with a suppression level greater than 20 dB upto 24.2 GHz. The centre frequency of the filter is 5.68 GHz with a fractional bandwidth of 97.57%. The fabrication process is carried out using MITS 11 Autolab fabrication machine with the low cost FR4 substrate and verified the performance improvement of the developed filter.