Low‐loss compact diplexer based on complementary spiral resonators

The article describes a novel low-loss microwave diplexer based on compact planar filtering elements. These are composed of spiral resonators and etched directly onto the signal layer. Furthermore, their design and optimization prove to be easy, and their native high-pass/low-pass characteristics are perfectly suited for assembling a diplexer. To verify the claim, a diplexer is designed and fabricated. It operates at 1.9 GHz and 3.5 GHz, and it is intended for personal communications service and 5G applications. The proposed device has an active area of 15.5 mm x $\times $ 19.5 mm. It shows an insertion loss of 0.35 dB and 0.28 dB for the two channels, representing the lowest data reported in the literature for this kind of device and technology. Additionally, the -10 dB-fractional bandwidths for the lower and upper bandwidths are 40.6% and 20.2%, respectively, and isolation is at least 25 dB for both channels.