Novel Diplexer and Triplexer Designs Avoiding Additional Matching Circuits Outside Filters

Diplexers and triplexers are widely used in communication systems for separating frequency bands in different channels. Design issues related to preventing additional matching circuits, integrating two or three band input resonators into one-band resonator size, systematically designing each band external quality factor (Q
_L
), and avoiding loading effects are often encountered. To overcome these bottlenecks, stub-loaded resonators that feature in various negligible band loading effects are used to design proposed diplexers and triplexers. In particular, the stub-loaded resonator (SLR), used in the proposed triplexers and costing only one-band resonator size, achieves a negligible loading effect systematic procedure for designing the three bands required as external quality factors and resonant frequencies. Each SLR of the triplexers uses an integrated matching circuit in the resonator instead of an additional matching circuit outside the resonator. To our knowledge, a tapped-line feed resonator that can independently design three band external quality factors (Q
_Ls
) and meet matching requirements by using one-band resonator size has not been reported thus far. All the currently proposed circuits have been verified and fabricated on RO4003C substrates.