Design of miniature wideband interdigital filters

In this paper a practical design procedure is suggested for designing wideband miniature interdigital filters. The proposed design approach is based on a concept of parameter mapping between two wideband filters, i.e. a conventional interdigital filter with uniform impedance resonators (UIR) and a desired miniature interdigital filter using stepped impedance resonators (SIR), allowing filter designers to deploy traditional designs with powerful electromagnetic (EM) simulators. For demonstration, a five-pole SIR interdigital filter with a fractional bandwidth (FBW) of 25% has been designed, fabricated, and tested. The demonstrator shows an excellent performance, which matches well to that of its conventional counterpart so as to validate the proposed design procedure.