E-Plane Tee vs H-Plane Tee
E-Plane Tee vs H-Plane Tee
In microwave engineering, waveguide tee junctions are important three-port microwave components used for power division, signal combining, and phase control. Two fundamental types of waveguide tee junctions are the E-plane tee and the H-plane tee. Although both devices contain two collinear ports and one side arm, their electromagnetic behavior is different because the side arm is positioned in different field planes.
The most important distinction between an E-plane tee and an H-plane tee is the phase relationship between the signals appearing at the two collinear ports when the side arm is excited. An E-plane tee produces equal-magnitude signals with opposite phase at the two collinear ports, whereas an H-plane tee produces equal-magnitude signals with the same phase. This difference makes the E-plane tee particularly useful for difference operations and the H-plane tee useful for sum or in-phase power division operations.
The fundamental phase relationships can be summarized as
$\boxed{\text{E-plane tee: equal magnitude, opposite phase}}$
and
$\boxed{\text{H-plane tee: equal magnitude, same phase}}$
These relationships form the basis for distinguishing the two junctions in microwave circuits and are particularly important when analyzing the S-parameter matrices of waveguide tees.
Basic Structural Difference
Both the E-plane tee and H-plane tee are three-port waveguide junctions. Two of the ports lie along the main waveguide and are therefore called the collinear ports. The third port is a side arm. The difference between the two structures is the plane in which this side arm is connected to the main waveguide.
In an E-plane tee, the side arm is connected to the main waveguide in such a way that it lies in the electric-field plane of the dominant waveguide mode. Because of this arrangement, the E-plane tee is also commonly described as a series tee or voltage tee.
In an H-plane tee, the side arm lies in the magnetic-field plane of the dominant waveguide mode. It is therefore commonly described as a shunt tee or current tee.
The names E-plane and H-plane therefore originate from the electromagnetic field orientation associated with the side arm. The distinction is not simply a matter of physical geometry; it directly affects the relative phase of the signals coupled into the two collinear ports.
Phase Relationship Between the Collinear Ports
The phase relationship is the most important property for comparing an E-plane tee and an H-plane tee. Consider the situation in which the side arm is excited while the two collinear ports are terminated under identical reference conditions.
For an E-plane tee, the two collinear ports receive signals having equal magnitude but opposite phase. The phase difference between the two signals is therefore
$\boxed{\Delta\phi_E=180^\circ}$
If the corresponding coupling coefficients are represented using a conventional reference-phase choice, the relationship can be written as
$\boxed{S_{1E}=-S_{2E}}$
The negative sign represents the phase reversal between the two collinear-port signals.
For an H-plane tee, excitation of the side arm produces equal-magnitude signals at the two collinear ports that are in phase. Therefore, the phase difference is
$\boxed{\Delta\phi_H=0^\circ}$
Under a consistent conventional reference-phase choice, this relationship can be written as
$\boxed{S_{1H}=S_{2H}}$
Thus, the fundamental distinction is
$\boxed{\text{E-plane tee: }S_{1E}=-S_{2E}}$
$\boxed{\text{H-plane tee: }S_{1H}=S_{2H}}$
The exact signs of individual S-parameters can depend on the selected port reference-plane and field-phase conventions. Therefore, the physically meaningful property is the relative phase: opposite phase for the E-plane tee and equal phase for the H-plane tee.
Power Division and Power Combining
Both types of tee can operate as power dividers or combiners. Under ideal symmetric conditions, excitation of the side arm divides the incident power equally between the two collinear ports. Therefore, each collinear port receives one-half of the available incident power when the junction is appropriately matched and lossless.
The important difference is not the amount of power delivered to each port but the phase relationship of that power.
For an ideal E-plane tee, the two output waves have equal magnitude and opposite phase. This makes the E-plane tee suitable for producing or combining difference signals.
For an ideal H-plane tee, the two output waves have equal magnitude and equal phase. This makes the H-plane tee suitable for producing or combining sum signals.
The distinction can therefore be represented conceptually as
$\boxed{\text{E-plane tee} \rightarrow \text{difference operation}}$
$\boxed{\text{H-plane tee} \rightarrow \text{sum operation}}$
This sum and difference interpretation becomes especially important when E-plane and H-plane tees are combined to form more advanced microwave components such as the magic tee.
E-Plane Tee and H-Plane Tee as Sum and Difference Ports
The phase behavior of the two tees gives them complementary roles in microwave signal combining and splitting. Suppose two signals are applied to the collinear ports. An H-plane tee responds to the in-phase component of these signals, while an E-plane tee responds to the out-of-phase or difference component.
For two input signals represented by \(V_1\) and \(V_2\), the sum and difference quantities can be represented conceptually as
$\boxed{V_{\text{sum}}\propto V_1+V_2}$
and
$\boxed{V_{\text{difference}}\propto V_1-V_2}$
When two equal signals are applied in phase, their sum is reinforced while their difference is ideally cancelled. Consequently, the H-plane tee is associated with the in-phase or sum response.
When two equal signals have a \(180^\circ\) phase difference, their difference component is reinforced while their sum component is ideally cancelled. Consequently, the E-plane tee is associated with the difference response.
This property is one of the main reasons why E-plane and H-plane tees are used together in microwave networks. Their complementary phase behavior allows a microwave system to separate or combine signals according to their phase relationship.
Comparison of E-Plane Tee and H-Plane Tee Properties
| Property | E-Plane Tee | H-Plane Tee |
|---|---|---|
| Basic type | Three-port waveguide junction | Three-port waveguide junction |
| Side-arm plane | E-plane | H-plane |
| Common name | Series tee or voltage tee | Shunt tee or current tee |
| Side-arm excitation | Produces equal-magnitude, opposite-phase waves at the collinear ports | Produces equal-magnitude, in-phase waves at the collinear ports |
| Phase difference | \(180^\circ\) | \(0^\circ\) |
| Ideal coupling relationship | \(S_{1E}=-S_{2E}\) | \(S_{1H}=S_{2H}\) |
| Power division | Equal power division under ideal symmetric conditions | Equal power division under ideal symmetric conditions |
| Combining behavior | Difference or cancellation operation | Sum or in-phase combining operation |
| Collinear-port output phase | Opposite phase | Same phase |
| Typical conceptual role | Difference port | Sum port |
| Important application | Phase-sensitive signal combining and difference operations | Power splitting, summing, and in-phase combining |
Difference in S-Parameter Behavior
The S-parameter matrices of E-plane and H-plane tees reflect their different phase relationships. For a reciprocal three-port network, the S-matrix is symmetric when the same reference conditions are used. However, the coupling coefficients associated with excitation of the side arm have different relative signs for the two types of tee under a conventional reference-phase choice.
For the H-plane tee, if the H-arm is designated as Port 3, the characteristic relationship is
$\boxed{S_{13}=S_{23}}$
This means that excitation of Port 3 produces equal-phase responses at Ports 1 and 2.
For an E-plane tee, if the E-arm is designated as Port 3, the corresponding relationship has opposite signs under the conventional phase reference:
$\boxed{S_{13}=-S_{23}}$
This indicates that excitation of the E-arm produces a \(180^\circ\) phase difference between the waves at the two collinear ports.
Therefore, when identifying an unknown ideal tee S-matrix, the relative signs of the two side-arm coupling coefficients can provide an important clue. Equal signs indicate the H-plane type under the chosen conventional reference, whereas opposite signs indicate the E-plane type. However, the reference-phase convention must always be kept consistent when interpreting individual S-parameter signs.
E-Plane Tee vs H-Plane Tee in Microwave Applications
The different phase characteristics of the two tees make them useful for different microwave functions. An E-plane tee is useful when a circuit requires a controlled phase reversal between two signal paths. Its opposite-phase output behavior makes it suitable for difference-type operations, cancellation, and phase-sensitive microwave networks.
An H-plane tee is useful when equal-phase signal distribution or combining is required. Its in-phase output behavior makes it suitable for power division, signal summing, and microwave networks in which the two output paths must maintain the same phase relationship.
Neither tee should be considered universally superior. The appropriate junction depends on whether the microwave system requires an in-phase or out-of-phase relationship between the collinear ports. In practical waveguide systems, the physical dimensions, matching, bandwidth, and reference-plane locations also influence the exact S-parameters.
E-Plane Tee vs H-Plane Tee: Key Point for Examinations
The most important examination distinction is the phase relationship produced when the side arm is excited. An E-plane tee produces two collinear-port signals of equal magnitude but opposite phase, whereas an H-plane tee produces two collinear-port signals of equal magnitude and equal phase.
The essential relationships can therefore be remembered as
$\boxed{\text{E-plane tee} \rightarrow 180^\circ\text{ phase difference}}$
$\boxed{\text{H-plane tee} \rightarrow 0^\circ\text{ phase difference}}$
The corresponding conceptual functions are
$\boxed{\text{E-plane tee} \rightarrow \text{difference}}$
$\boxed{\text{H-plane tee} \rightarrow \text{sum}}$
Thus, the E-plane tee and H-plane tee are complementary microwave junctions. Their main difference is not simply their physical orientation but the electromagnetic phase relationship they impose between the two collinear ports. This phase behavior determines their role in power division, signal combining, phase cancellation, and more advanced microwave components.