Super Compact (<1cm2) Band Pass Filters with Wide Bandwidth and High Selectivity at C-band

In this work, it is demonstrated that planar microwave filters operative at C-band can be realized with simultaneously very small dimensions (area A<1cm
²
), wide bandwidth (fractional bandwidth FWB>45%) and high frequency selectivity (transition bands with more than 50dB/GHz fall-off at both band edges). This is possible thanks to the development of new innovative concepts for planar filter design. Specifically, we have considered two alternative approaches: (i) one based on the use of metamaterial resonators, such as complementary split rings resonators (CSRRs), combined with inductive stubs and series gaps, and (ii) another based on semi-lumped resonators coupled through 90deg meanders lines acting as admittance inverters. In both cases, key to achieve the small dimensions is the sub-wavelength operation of the resonant elements. The simultaneous optimisation of performance and dimensions that can be achieved through both approaches is unique and, for this reason, it is believed that the ideas presented in this work can be of actual interest in practical applications