Compact Branch-Line Coupler Layout for PCB Area Reduction

The patent applies curvature by replacing straight quarter-wavelength transmission lines with bent transmission lines. The bent lines achieve the same electrical length (quarter-wavelength at center frequency) while occupying less physical space on the PCB. This resolves the contradiction by maintaining coupling performance through proper electrical length while reducing the actual area occupied.

The patent utilizes multi-layer PCB construction to route transmission lines in different physical layers. By transitioning from a single-plane layout to a three-dimensional multi-layer configuration, the coupler achieves the required electrical characteristics with reduced footprint on each individual layer, effectively solving the area constraint while maintaining performance.

The patent systematically adjusts multiple parameters including line width, spacing between parallel lines, bend angles, and lengths of straight and curved sections to achieve the target characteristic impedance. By carefully controlling these geometric parameters during the design phase, the bent transmission lines maintain proper impedance matching despite their non-straight configuration, resolving the contradiction between size reduction and impedance control.

The patent applies different geometric configurations to different sections of the transmission lines. Straight sections maintain consistent impedance, while bent sections are specifically designed with appropriate curvature radii and transition regions. This localized optimization of geometry ensures that impedance control is maintained throughout the entire signal path despite the overall bent configuration, achieving both size reduction and impedance precision.