The Synthesis of a Class of Branch-Line Directional Couplers

• Published in: IEEE transactions on microwave theory and techniques Vol. 56; no. 8; pp. 1985 - 1994
• Main Author: Fathelbab, W.M.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01-08-2008; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Bandwidth; Branch-line couplers; Circuit optimization; Circuit properties; Circuit synthesis; Couplers; Coupling circuits; Devices; Directional couplers; Dual band; Electric, optical and optoelectronic circuits; Electronics; Exact sciences and technology; Filtering theory; Joining; Microstrip; Microwave circuits, microwave integrated circuits, microwave transmission lines, submillimeter wave circuits; Microwaves; network prototypes; Network synthesis; Prototypes; Synthesis; transmission zeros; Performance evaluation; Microwave coupler; Prototype; Branch-line couplers; Coupled line; network prototypes; Implementation; transmission zeros
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2008.927407

The design of a class of branch-line couplers comprising coupled-line branches is presented. The method employs classical network synthesis to derive a distributed network prototype from which the modal sub-networks of the coupler are found. The branch-line couplers overcome realization difficulties that are often encountered with conventional couplers. The synthesis of a 3-dB branch-line coupler is presented in detail and further implemented on a microstrip board. The measured performance of the fabricated device shows close agreement with the underlying theory.