I. Introduction
Intensive research efforts have been put on the design of multiband filters to face the challenges related to services requiring several frequency bands or reconfigurable devices. The most popular approaches to design dual-band filters are based on the split of wideband filters [1], the manifold or star-junction connection of different filters [2], and the use of multimode resonators [3]. On the other hand, different synthesis methods have been proposed using an even symmetry frequency mapping between the single- and the dual-band domain [4], [5]. However, the symmetric mapping yields a phase function with odd symmetry which is not suitable to carry out the dual extracted pole.