Dual-band bandpass filter using integrated open loop resonators with embedded ground slots

In this article, a dual-band bandpass filter is proposed using two half wave length open loop resonators integrated in concentric topology. The outer set of resonators are realized to operate at lower pass band of 2.4 GHz which is coupled directly to input and output ports where as the inner set of resonators are designed at 3.5 GHz which is electromagnetically coupled to the outer resonator. To obtain wide passbands, enhanced coupling between the outer resonators is realized using ground slots just below the open loop sections of the resonators. The measured passband bandwidth at 2.45 and 3.5 GHz is 187 and 155 MHz respectively. Four transmission zeros, created due to source load coupling, are located close to the passband edges at 2.18, 2.68, 3.38, and 3.72 GHz to increase skirt selectivity. Over all filter dimension is 20 mm by 32 mm. An equivalent circuit model is developed that is in close agreement with full wave simulation and measured results. (C) 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2049-2052, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26991