A Novel Triple-Band Microstrip Branch-Line Coupler With Arbitrary Operating Frequencies

This letter presents a novel microstrip branch-line coupler operating in three frequency bands. The design methodology of the triple-band branch-line coupler is established by using a compensation technique to improve the matching property within each passband region. The proposed coupler with compact size is realized by folded microstrip open-circuited and short-circuited stubs. The measured, full-wave simulated and equivalent-circuit modeled results illustrate good agreement among them, which validates the design method and shows the advantages of deep rejection between each operating frequency, and the dc grounded input and output ports.