Design of a compact diplexer for multisystem DAS solutions

This paper presents a microstrip diplexer for multisystem Distributed Antenna System (DAS) solutions, namely for DCS and UMTS systems. A low-pass quasi-elliptic filter with a stub-like structure is used for the 1800 MHz band while a band-pass Chebychev filter with a hairpin line structure is employed for the 2150 MHz band. Both filters are connected to the common port through a T junction. The diplexer layout has been optimized in order to ensure compactness. Good agreement between simulated and measured results has been obtained. The diplexer shows excellent performance in terms of high isolation and low insertion loss. A semi-lumped element model of the diplexer is also presented.