Wideband Bandpass Filters Using a Novel Thick Metallization Technology

A new class of wideband bandpass filters based on using thick metallic bars as microwave resonators is presented in this work. These bars provide a series of advantages over fully planar printed technologies, including higher coupling levels between resonators, higher unloaded quality factors <inline-formula> <tex-math notation="LaTeX">$Q_{U}$ </tex-math></inline-formula>, and larger bandwidths implemented with compact structures. In comparison to dielectric and waveguide resonators filters, higher bandwidths together with lower weight and footprint reduction are achieved with the proposed thick bars technology. Moreover, thick bar resonators can easily be coupled to an additional resonance excited in a box used for shielding, allowing to realize transversal topologies able to implement transmission zeros at desired frequencies. To illustrate the capabilities of this technology, three microwave filters with different topologies have been designed. One of the designed filters has been manufactured and tested using copper bars inside an aluminum housing partially filled with Teflon. Measured data demonstrates a fractional bandwidth of <inline-formula> <tex-math notation="LaTeX">$FBW=32\%$ </tex-math></inline-formula>, spurious free range <inline-formula> <tex-math notation="LaTeX">$SFR>50\%$ </tex-math></inline-formula>, unloaded quality factor of <inline-formula> <tex-math notation="LaTeX">$Q_{U}=1180$ </tex-math></inline-formula>, insertion losses over 0.16 dB and return losses over 20 dB, without requiring any post-tuning operation on the prototype. This result confirms the exciting performance of the proposed technology for wideband applications.