Miniaturized bandpass filter with wide stopband using complementary spiral resonator

In this paper complementary spiral resonators are used in the design of compact planar bandpass filters with wide upper stopband. Based on an inductively loaded transmission line model for the complementary spiral resonators it is shown that the ratio of the spurious resonant frequency to the fundamental resonant frequency can be increased. Comparing two filters realized by conventional open-loop resonators and complementary spiral resonators it is shown that the utilization of complementary spiral resonators not only results in a more compact filter but also that a wide upper stopband is achieved.