H-Plane Tee (Shunt Tee)
Understanding the H-Plane Tee
In microwave engineering, splitting an RF signal requires a junction. The H-Plane Tee is one of the two fundamental waveguide splitters. It earns the name "H-Plane" because the new branch connects parallel to the Magnetic (H) field lines of the dominant TE₁₀ waveguide mode. Because of its geometric construction on the narrow wall, it electrically behaves like a parallel (shunt) circuit.
The 0-Degree Phase Split (In-Phase)
The most important characteristic of the H-Plane Tee is how it handles phase. Imagine feeding a radar pulse down the vertical arm of the "T" (Port 3). When the wave hits the far wall of the main waveguide, it splits left to Port 1 and right to Port 2.
Unlike the E-Plane tee, the electric field vector in an H-Plane tee does not flip directions. If the electric field arrow is pointing "up" in the vertical arm, it continues pointing "up" as it splits into both the left and right arms. Mathematically, this means the two output signals are identical in power and perfectly 0 degrees in phase.
S₂₃ = S₁₃
What this means:
If you input 100 Watts at Port 3 (the vertical arm):
- Port 1 outputs 50 Watts at 0° phase.
- Port 2 outputs 50 Watts at 0° phase (indicated by the positive sign, meaning no phase difference).
The Sum Port (Addition)
Like all passive RF components, an H-Plane Tee is reciprocal. It can be used to split a signal, or combine two signals. What happens if you pump two signals into the side arms (Port 1 and Port 2) and extract the result from the vertical arm (Port 3)?
- If the two input signals are perfectly in-phase, they constructively combine at the junction. The full power exits Port 3.
- If the two input signals are exactly 180-degrees out of phase, they will destructively interfere and perfectly cancel each other out at the junction. The output at Port 3 will be zero.
For this reason, when an H-Plane Tee is used as a combiner, it acts as an adder. Port 3 is often referred to as the Sum Port or the Sigma ($\Sigma$) port in advanced radar networks.
E-Plane vs. H-Plane Summary
| Feature | H-Plane Tee (Shunt) | E-Plane Tee (Series) |
|---|---|---|
| Attachment Wall | Narrow Wall | Broad Wall |
| Power Split (from Branch) | Equal (50% / 50%) | Equal (50% / 50%) |
| Phase Shift | 0° (In-phase) | 180° (Out of phase) |
| Combining Action | Adds signals (Sum Port) | Subtracts signals (Difference Port) |
Frequently Asked Questions
Why is it called an H-Plane Tee?
It is named based on its geometry relative to the electromagnetic field. The auxiliary branch (the vertical arm of the "T") is attached to the narrow wall of the waveguide, which is parallel to the Magnetic (H) field lines of the dominant TE10 mode.
Why do the outputs have a 0-degree phase shift?
Unlike the E-Plane tee which forces the electric field to bend in opposite directions, the H-Plane tee splits the wave along the magnetic field. The electric field vector remains pointing in the same direction (e.g., straight up) in both output arms, meaning the waves are perfectly in-phase.
What happens if I feed signals into both colinear arms at the same time?
If you feed two identical, in-phase signals into the two horizontal arms, they will combine constructively at the vertical H-arm because of the 0-degree phase property. The H-arm becomes a "sum" port.