Reduced-length uniplanar bandpass filters based on coplanar-waveguide-slotline tees

This paper presents the design and implementation of multimodal uniplanar bandpass filters which use loaded coplanar-waveguide-slotline tees in the slotline resonators to reduce the filter length. The tees are theoretically analyzed to obtain a multimodal model, and applied to the design of two second-order bandpass filters at 1.5 GHz, one with reduced length and the second with compact dimensions (0.16λ × 0.069λ). The filter measurements validate the theory, exhibiting an insertion loss of 1.55 dB (reduced-length filter) and 2.6 dB (compact filter) with a 8% bandwidth.