Planar Diplexer Design Using Hairpin Resonators Loaded with External Capacitors for Improvement of Isolation and Stopband Rejection Levels

We have successfully demonstrated the design and implementation of a planar diplexer operating at 900MHz and 1800MHz intended for cellular system applications. Using hairpin resonators loaded with external capacitors, we managed to obtain 40% size reduction compared to the ones without external loading with substantial improvement in the band-to-band isolation.