A Simple f0/2f0 Microstrip Diplexer with Low and Wideband Insertion-Loss Characteristics

Ken'ichi HOSOYA
Ryosuke EMURA

IEICE TRANSACTIONS on Electronics   Vol.E104-C    No.1    pp.11-21
Publication Date: 2021/01/01
Publicized: 2020/06/22
Online ISSN: 1745-1353
DOI: 10.1587/transele.2020ECP5016
Type of Manuscript: PAPER
Category: Microwaves, Millimeter-Waves
diplexer,  duplexer,  microwave,  microstrip line,  coupled line,  wideband,  insertion loss,  

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An f0/2f0 (frequency ratio of two) microstrip diplexer with simple circuit configuration as well as low and wideband insertion-loss characteristics is proposed. It is a parallel combination of a coupled line for f0 port and a wave-trap circuit composed of a transmission line and an open stub for 2f0 port. All the lines and stub have a quarter-wave length for f0. Matching circuits are not needed. Circuit and electro-magnetic simulation results prove that the proposed f0/2f0 diplexer exhibits well-balanced properties of insertion loss (IL), IL bandwidth, and isolation, as compared to conventional simple f0/2f0 diplexers composed of two wave-trap circuits or two coupled lines. The proposed diplexer is fabricated on a resin substrate in a microstrip configuration at frequencies of f0/2f0=2.5/5 GHz. Measured results are in good agreement with simulations and support the above conclusion. The proposed diplexer exhibits ILs of 0.46/0.56 dB with 47/47% relative bandwidth (for f0/2f0), which are lower and wider than f0/2f0 diplexers in literatures at the same frequency bands.