A Symmetrical Fractal-based Balanced Branch-Line Coupler for Simultaneous Low- and Mid-band 5G Frequencies Applications

• Published in: Applied Computational Electromagnetics Society journal Vol. 38; no. 12; pp. 965 - 974
• Main Authors: Shallah, Abdulkadir B., Zubir, Farid, Rahim, Mohamad Kamal A., Yusoff, Zubaida
• Format: Journal Article
• Language: English
• Published: Pisa River Publishers 16.04.2024
• Subjects: Beamforming; Broadband; Couplers; Crosstalk; Fractals; Frequencies; Frequency ranges; Impedance matching; Phase sensitive detectors; Substrates; Symmetry
• ISSN: 1054-4887; 1943-5711
• DOI: 10.13052/2023.ACES.J.381206

Symmetry is a key factor for Branch-Line Couplers (BLCs) in RF and microwave systems. This balanced approach evenly distributes power between two output ports, aiding impedance matching and reducing unwanted coupling and crosstalk, while increasing input-output isolation. Furthermore, the symmetrical design of BLCs ensures favorable return loss and phase balance, which are essential for phase-sensitive detectors and beamforming. This symmetry also guarantees consistent performance over a wide frequency range, making it suitable for broadband or multi-frequency applications. We present a compact BLC operating in two frequency bands, ideal for 5G sub-6 GHz applications. It uses T-shaped lines with folded lines and stubs in a Minkowski fractal shape, resulting in a size reduction of 90%. The design and simulation were performed using the CST Microwave Studio at 0.7 GHz and 3.5 GHz, achieving a new high frequency band ratio of 5. A prototype on Rogers RT5880 substrate (εr=2.2,h=0.787 mm) was tested to validate the design’s effectiveness, offering potential for modern wireless applications requiring versatile frequency band operation.