Four Spiral Resonator Compact Diplexer with Improved Out-of-Band Rejection for the Coexistence of 5G Applications

A diplexer with two channels and two resonators per channel is presented. A new arrangement for the resonators is proposed. The geometry of the resonators is based on two kinds of spiral shapes corresponding to two different filtering behaviors: open spirals (low pass) and etched spirals (high pass). To show the effectiveness of the design, a prototype is realized for 5G applications. The prototype works at 2.26 GHz and 3.59 GHz and at the lower [higher] frequency channel is characterized by a return loss of 13.4 dB [15.0 dB], an IL of 1.1 dB [1.2 dB], an isolation of 34.2 dB [38.2 dB], and a fractional bandwidth of 39.7 % [7.5 %]. The active area is 19.5 mm×25 mm. Out-of-band rejection is −41 dB and −37 dB for the lower and higher channels, respectively. The ratio between out-of-band rejection and occupied area is one of the highest among previously published diplexers using the same technology.