Design of a Shielded Microstrip-Line Diplexer Capable of DC Signal Transmission

This paper proposes a shielded microstrip-line diplexer capable of DC signal transmission between all ports. To secure DC transmission paths, a continuous signal-line structure connecting all ports is employed. In addition, the circuit is configured only with transmission lines and open stubs, without using short-circuited stubs, to prevent DC short-circuit paths. To suppress undesired electromagnetic coupling between adjacent signal lines and stubs in the pass band, metallic partition walls are inserted to provide physical shielding and minimize mutual coupling. The proposed diplexer has a receiving band of 1.69-1.78GHz and a transmitting band of 2.11-2.18GHz. The simulated results show an in-band return loss of less than –14.09dB, an insertion loss of greater than -0.53dB, an attenuation characteristic of less than -51.49dB, and an isolation characteristic of less than -52.53dB. The overall size of the proposed diplexer is 138.7 × 139.7 × 17.2 [mm³ ].