Using Dielectric Rods to Reconfigure Combline Filters in Center Frequency and Bandwidth

This article describes the use of dielectric rods to reconfigure combline filters both with respect to center frequency and bandwidth. In this context, a new filter topology is developed in order to maximize the achievable reconfiguration range. The design of a prototype is discussed in detail, clearly demonstrating the feasibility of center frequency and bandwidth reconfiguration, with the same filter structure, while maintaining an equiripple return loss. In addition to theory, a combline filter prototype is also fabricated, tuned and measured in several configurations showing excellent agreement with simulations, thereby fully validating both the basic concept and the design procedure.