Waveguide Bandpass Filters made of Thick Complementary Small Resonators
  We explore the potential use of complementary split ring resonators (csrr's) and complementary spirals of two and three turns (csr2 and csr3) to design very compact waveguide filters. We demonstrate its passband response in an experimental and computational form. Besides, it is shown that the design process can be highly simplified by means of a new waveguide model that reduce full wave numerical simulations. Thus, it is possible to design waveguide filters with lengths equal to the thickness of a metallic sheets, leading to an improvement in the design of miniaturized waveguide filters. 
Laura Maria Pulido Mancera and Juan Domingo Baena Doello
physics.optics