Methods, systems, and devices are described for improving a performance of a waveguide device. A waveguide device that includes a common port and divided ports may also include a sidewall feature that extends across a first set of opposing sidewalls and a second set of opposing sidewalls of the waveguide device. The sidewall feature may have a same shape on each of the first set of opposing sidewalls and a second set of opposing sidewalls. In some cases, the sidewall feature is positioned outside a divided waveguide section of the waveguide device. The position of the sidewall feature may be determined based on an impedance matching metric between the common port and the divided ports, an isolation metric between the divided ports, or both.