Single-Sided Filters in Microstrip Technology

This paper describes how to approach the design of microstrip filters with requirements in one passband and one stopband, both of finite extension (single-sided filters). Suitable filter topologies have been investigated, which allow having the filter passband either above or below the filter stopband. A design procedure, originally developed for waveguide single-sided filters, has been adapted also for this class of filters; the designed filters exhibit a quasi equiripple response both in the passband and in the stopband. The procedure has been first verified with electromagnetic simulations (using planar commercial simulators); then, using the proposed approach, a test microstrip filter in the DCS 1800 cellular band has been designed and fabricated employing standard PCB technology; the measurements have shown a satisfactory agreement with the simulations.