A Novel Compact Broadband Quasi-Twisted Branch Line Coupler Based on a Double-Layered Microstrip Line.

Area of Science:

• Electrical Engineering
• Electromagnetics
• Microwave Engineering

Background:

• Branch line couplers (BLCs) are fundamental components in microwave circuits.
• Conventional BLCs often suffer from large physical dimensions, limiting their integration into compact systems.
• Miniaturization and wideband performance are critical for modern wireless communication systems.

Purpose of the Study:

• To propose and demonstrate a novel, miniaturized wideband branch line coupler (BLC).
• To achieve significant size reduction compared to conventional BLCs while maintaining wideband characteristics.
• To evaluate the performance of the proposed BLC for potential use in 5G beamforming networks.

Main Methods:

• A quasi-twisted design approach by bisecting and folding a conventional microstrip line BLC onto a double-layered substrate.
• Utilizing Z-shaped meandered microstrip lines for input/output terminals and horizontal arms.
• Employing a periodically loaded slow-wave structure for vertical arms and connecting bisected parts via vias.
• Fabrication on a low-cost FR4 substrate.

Main Results:

• Achieved a compact BLC size of 6.4 × 18 mm², representing a ~50% miniaturization compared to conventional designs.
• Attained a relative bandwidth of 73.9% (4.6-10 GHz) for key parameters.
• Demonstrated excellent isolation of -13 dB and transmission coefficients between -3.1 dB to -3.5 dB at 6 GHz.
• Achieved output port phase differences of 90.5° and 94.8°.

Conclusions:

• The proposed quasi-twisted miniaturized BLC offers significant size reduction and wideband performance.
• The design is suitable for integration into compact microwave circuits and systems.
• The BLC shows potential as a unit cell for Butler matrices in sub-6 GHz 5G beamforming networks.