An analysis of a width-modulated microstrip periodic structure

The wave propagation along a microstripline with sinusoidally varying width has been investigated. The analysis employs the circuit theory of uniform microstriplines and their step junctions. The wave amplitude transmission (WAT) matrix has been successfully used to determine the propagation constant, characteristic impedance, and the input impedance of the terminated line. Samples have been fabricated for the experimental verification of the above-mentioned quantities. Theory and experiment show good agreement. The filter-like propagation characteristic of the structure is exploited in the realization of a bandstop filter. A graphical design of such a filter is presented and the insertion-loss measurement shows encouraging results.