Single and dual band bandpass filters using complementary split ring resonator loaded half mode substrate integrated waveguide

High performance microwave bandpass filters with low insertion loss, high selectivity, compact size and multiple bands are widely used for wireless and satellite communication systems [1]. During the years, bandpass waveguide filters have used all kinds of metallic and non-metallic insertions in order to improve performance and reduce size [2]. Since the first experimental demonstrations of metamaterial particles exhibiting either negative permeability such as the split ring resonators (SRR), or negative permittivity such as the complementary split ring resonators (CSRR), different implementations combining waveguide with such structures have been widely investigated for bandpass filters [3-4], mainly motivated by their extraordinary property of generating backward wave transmission below the waveguide cutoff frequency. On the other hand, the need for new applications and integration with digital circuitry is the motivation for proposing and implementing planar microwave filters with performances similar to those provided by the bulky waveguide filters. The substrate integrated waveguide (SIW) and the half mode substrate integrated waveguide (HMSIW) [5-6] have been selected as the key wave guiding structures for the implementation of low loss, high quality factor and improved selectivity waveguide bandpass filters on printed circuit board (PCB) technology. In addition, taking into account the possibility of having forward wave propagation below the waveguide cutoff frequency, the substrate integrated waveguide has been combined with complementary split ring resonators (CSRR) for the implementation of compact size and high selectivity bandpass filters [7].