The hybrid quadrature coupler (also called a branchline coupler) is a classic microwave device. It splits the power in half between two outputs. The output signals have a phase difference of 90°, which is used both in transceivers and in antenna technology, for example, to create circularly polarized antennas. Unlike the 3dB coupled microstrip coupler, it is easily implemented in a PCB version. However, the implementation of PCB microwave designs with substrates available to radio amateurs is almost impossible, this is a matter for professionals, so we offer here the calculation of a “low-frequency” version of such a divider/combiner on lumped elements.
In this circuit, all four waveguides of the quadrature coupler are replaced by an equivalent circuit of a Pi-shaped LC low-pass filter with a cutoff frequency equal to the operating frequency of the quadrature divider. In this case, the required phase delay is realized.
JavaScript source code: Copyright ©2025 3G-Aerial
Calculation formulas:
The port matching in the hybrid quadrature coupler is very good, the isolation between the output ports can be more than 30 dB, but the bandwidth is somewhat smaller than, for example, in a Wilkinson divider.
Related links:
- Branchline Couplers - microwaves101.com;
- A Quad-Mode Analysis of the qudrature hybrid coupler - The University of Kansas [PDF];
The site has comments on social networks, which have much more opportunities for communication.