Mutually-Tapped Coupling between Combline Resonator Pairs for Ultra-Wideband (UWB) Filter Realization

Abstract

In this paper, a novel ultra-wideband filter in the form of λ/4 microstrip resonator is proposed. The key technique is to use a mutually-tapped coupling schematic, which utilizes a short line to connect two combline resonators at a certain height. It is capable of achieving very wide coupling bandwidth, thus useful in realizing wideband filter in microstrip form. The coupling coefficient can be calculated by an odd-even mode analysis. A filter with a passband covering 8.5–13 GHz is designed, fabricated and measured. It has the advantage of compact size, and, as an interesting phenomenon, the filter response is asymmetrical because of the existence of crosscouplings. The agreement between simulated and measured results has validated the feasibility of the proposed filter.