Waveguide Tees: E-Plane vs. H-Plane

Waveguide tees are essential components in microwave engineering, serving the crucial function of signal splitting and combining. This article delves into E-plane and H-plane tees, explaining their working principles, illustrating their diagrams, highlighting their differences, and providing their S-matrix representations.

In RF and microwave circuits, a waveguide or coaxial line junction with three ports is known as a tee junction. These devices are primarily used for combining and splitting power within a waveguide system. Waveguide tees are 3-port components, mainly categorized into two types: E-plane tees (connected in series) and H-plane tees (connected in shunt) with a section or branch of the main waveguide transmission line.

Let’s explore the operations and functions of these waveguide tee types, including the key differences between them.

E-Plane Tee (Series Tee)

E plane tee

As shown in the E-plane tee diagram, the axis of the side arm is parallel to the E-field. This type of E-plane tee is often perfectly matched using screws or capacitive/inductive windows at the junction. When perfectly matched, reflections are minimized, and the diagonal S-parameters of the scattering matrix become zero (S11, S22, and S33 are zero).

For a matched junction, the S-matrix is represented in equation (1) (see Figure-1 in the original article). When waves are fed into port-3 (the side arm), the waves at port-1 and port-2 of the collinear arms will have the same magnitude but opposite phases. Hence, $S_{13} = -S_{23}$.

Note: Equation (1) represents an ideal perfectly matched junction, but in practice, matching may be imperfect.

The S-matrix when collinear arms are symmetric about the side arm is mentioned in equation (2). Here, $|S_{13}| = |S_{23}|$ and $S_{11} = S_{22}$.

H-Plane Tee (Shunt Tee)

H plane tee

As shown in the H-plane tee diagram, the axis of the side arm is parallel to the H-field (magnetic field). In an H-plane tee, when two inputs are fed into port-1 and port-2 of the collinear arms, the output at port-3 will be in phase and additive.

Conversely, if the input is fed at port-3, the waves are split equally into port-1 and port-2 with the same phase and magnitude. These characteristics of the H-plane tee are used in waveguide power combiners and power dividers.

The S-matrix representation of the H-plane tee is similar to that of the E-plane tee, as mentioned in equations (1) and (2) (see Figure-1 in the original article), except that here, $S_{13} = S_{23}$.

Due to imperfect matching, tuning screws are often used to adjust the reactance of the system to achieve perfect impedance matching.

Difference Between E-Plane and H-Plane Tee

Conclusion

E-plane and H-plane waveguide tees are essential for efficient signal management in microwave circuits. Understanding their unique features and applications ensures optimal usage in communication systems.