E- Plane Tee

We have studied how waveguides form an important part of microwave engineering. In this article, we will study one important application of waveguide which is E-Plane Tee. E-Plane Tee is a junction which is formed by joining two waveguides together. We will study the E-Plane Tee by looking at its properties and its structure.

We will also see how an E-Plane Tee operates. In addition to this, we will study the E-Plane Tee Circuit Model and its use in various feed systems. Later, we will study the advantages, disadvantages, and applications of E-Plane Tee. The article will conclude with some frequently asked questions that users can refer to.

E-Plane Tee

An E-Plane Tee also known as a waveguide Tee is a device made of two waveguides connected. It is made by joining a waveguide to another rectangular waveguide that already has two ports. Therefore, the shape of the whole device resembles the letter ‘T’ in the English alphabet, giving it the name ‘Tee’. The figure given below represents a basic E-Plane Tee.

E-Plane Tee

In an E-Plane Tee, the axis of the side arm is parallel to the Electric Field (E) of the collinear arms which is a critical property of this device. If we carefully observe, the E-plane Tee is a 3-port device. In general, the input is given at port 3 and then the signal is obtained from port 1 and port 2.

Properties of E-Plane Tee

We have seen that S-parameters or scattering parameters are used for describing the properties of appliances that use microwave frequencies. We can define a 3⨯3 scattering matrix to discuss the properties of E-Plane Tee. Each entry in this matrix will denote the relation between the ports. Therefore, S_ij depicts the relation between the i^th and the j^th port of the Tee.

Let there be a matrix S

S= [S₁₁ S₁₂ S₁₃ ]

. [S₂₁ S₂₂ S₂₃ ]

[S₃₁ S₃₂ S₃₃] Eq 1

In an E-Plane matrix, the output at ports 1 and 2 when input is fed at port 3 is out of phase by 180⁰ therefore, we can say that

S₂₃= -S₁₃ Eq 2

Since port 3 is perfectly matched to the junction, we can say by the properties of the matched junction that

S₃₃=0 Eq 3

From the symmetric property S_ij=S_ji so

S₂₁=S₁₂ S₂₃=S₃₂ S₁₃=S₃₁ Eq 4

Using the above-formed equations, we can rewrite the matrix S as

S= [S₁₁ S₁₂ S₁₃ ]

[S₁₂ S₂₂ -S₁₃ ]

[S₁₃ -S₁₃ 0] Eq 5

In this matrix, we have 4 unknowns. Now from the unitary property of lossless medium,

[S][S]*=[I]

Therefore [S₁₁ S₁₂ S₁₃ ] [S₁₁^* S₁₂^* S₁₃^*] = [1 0 0]

[S₁₂ S₂₂ -S₁₃ ] [S₁₂^* S₂₂^* -S₁₃^* ] = [0 1 0]

[S₁₃ -S₁₃ 0 ] [S₁₃^* -S₁₃^* 0 ] = [0 0 1]

On multiplying the matrix and equating the terms, we get

S₁₁S₁₁^*+ S₁₂S₁₂^*+S₁₃S₁₃^*=1

∴ |S₁₁|² + |S₁₂|²+ |S₁₃|²=1 Eq 6

Similarly

∴ |S₁₂|²+ |S₂₂|²+ |S₁₃|²=1 Eq 7

∴ S₃₁|²+|S₁₃|² = 1 Eq 8

∴ S₁₃S₁₁^*– S₁₃S₁₂^* =1 Eq 9

Now, we will equate the equations to derive relations

Equating 6,7

S₁₁= S₂₂ Eq 10

Also from eq 8

2|S₁₃|²=1

∴ S₁₃=1/√2 Eq 11

From eq 9

S₁₁= S₁₂= S₂₂ Eq 12

Using eq 10,11,12 in eq 6

|S₁₁|²+ |S₁₁|²+ 1/2 =1

∴ |S₁₁|=1/2

Now, we will substitute these values to get our final scattering matrix

[S]= [ 1/2 1/2 1/√2 ]

[ 1/2 1/2 -1/√2 ]

[1/√2 -1/√2 0 ]

This is known as the scattering matrix of E- Plane Tee which is used to study the properties of E- Plane Tee.

E-Plane Tee Structure

Given below is the structure of the E-Plane Tee

E-Plane Tee Structure

If we observe, we can see that the Tee consists of one rectangular waveguide with two ports namely port 1 and port- 2, and another waveguide is connected to the original waveguide which results in a ‘T’ structure. This waveguide results in a third port called port-3. There are mainly two parts in E-Plane Tee

Side Arm: The new arm due to the additional waveguide is called the side arm or the E arm. It has a 3^rd port i.e. port 3 on it. This arm is perpendicular to the side collinear arms.

Collinear Arms: The arms formed by the rectangular waveguide are called collinear arms. Port 1 and Port 2 lie on this arm. It is called collinear because both the ports lie on the same line i.e. these ports are collinear.

E-Plane Tee Operation

Let us now understand how the E-Plane tee operates with the help of a diagram.

E plane Tee operation

We know that a waveguide is a structure that helps to guide and propagate electromagnetic waves and tees combined with a waveguide help to combine or split these waves. In an E-plane Tee, the electromagnetic waves combine in a way that the propagation is perpendicular to the direction of the electric field. Let us see how it operates:

• Combining the incoming waves: In an E-Plane Tee, input is fed at any two ports. Suppose that the input is fed at port 2 and port 1 then the Tee will combine the two input fed. The combination of these two inputs will then be given as the output of the third port. Here the output will be generated from port 3. This is how E-plane Tee uses the 3 ports for the combining purpose.
• Splitting of incoming wave: In an E-Plane Tee, if the input is fed at any one port then the E-Plane Tee will perform the task of splitting this input wave equally at the junction and thus two waves of equal magnitude, and the opposite phase will be given as output from other two ports. For input fed at port 3, the input will split and output waves will be received at port 2 and port 1.

E-Plane Tee Circuit Model

Here is a circuit to illustrate the E-Plane Tee in a circuit

E-Plane Tee Circuit Model

• Co-Axial Cable: The ports of an E-Plane Tee are connected to other components of the circuit using a co-axial cable. Proper termination of co-axial cable is necessary to ensure impedance matching. The co-axial cable should be able to match the characteristic impedance of Tee. This is how cable ensures proper signal transmission.
• E-Plane Tee: The E-Plane Tee forms one essential component of the circuit. It performs the task of combining or splitting the input wave depending on the application it is being used for. The input is generally fed at port 3 and then the Tee splits the input to generate output at the two ports, port 1 and port 2.
• Terminations: At the end of each port reflections can occur and distort the signals therefore terminations are applied to minimize signal loss through reflections. This is how power is transmitted efficiently.
• Signal Monitoring: A probe can be used to measure the signal at certain points. The probe is connected in a way such that it helps to test the signal at a specific port without causing any trouble to the signal.

E-Plane Tee in Antenna Feed Systems

One of the major applications of E-Plane Tee is its use in antenna Feed Systems where it creates balanced feed networks. The term balanced feed is used to indicate equal and opposite currents in elements. This can be done by utilizing the properties of E-Plane Tee. Let us see how

The E-Plane Tee is a device used to distribute the incoming wave in different directions. This is applied in the antenna feed system to direct incoming signals to different antenna elements. In addition to the distribution of the signal to different elements, it allows us to control the phase of the signal developed across antenna elements. Therefore, the Tee’s ability to efficiently split signal gives the antenna directional characteristics and desired radiation pattern.

Not only this but the use of an E-Plane Tee in an Antenna Feed System can be done easily due to the compact structure of the Tee. The use of E-Plane Tee can help us to create phased array antennas that have constant magnitudes with symmetric phase differences. This is necessary to create a balanced radiation pattern that enhances the performance of the antenna.

E-Plane Tee in Network Analyzers

Network analyzers can be described as electrical instruments that are used to study the electrical characteristics of various components and networks. let us see how we can use E-Plane Tee to enhance the overall performance of Network Analyzers

The tee properties are utilized for the calibration of various devices. This is necessary to ensure that the measurements being made are free of errors. E-Plane Tees can be used as a standard or reference for other components being measured,various properties like scattering parameters are calculated.

In addition to this, E-Plane Tee assists Network Analyzers in the transmission and reflection of signals in the microwave range. E-Plane Tee can be used to control the reflection path of waves with the help of Network Analyzers. This is done by controlling the distribution of signals and then correctly analyzing the incident and reflected signals. Overall, using E-plane Tee in network analyzers can enhance the accuracy and therefore the performance.

Advantages of E-Plane Tee

Let us see some advantages of the E-Plane Tee

• E-Plane Tee provides us with the combined features of a tee and a waveguide therefore it offers a variety of features like combining and splitting the original signal depending on our needs.
• One major advantage of the E-Plane Tee is the low-cross coupling between the arms. Due to the configuration of the E-Plane Tee, the coupling between any two arms is minimal which is important for isolation.
• The symmetrical configuration of the E-Plane Tee simplifies the design of the tee. The output generated is the same irrespective of the port used for input. This helps to generate consistent output irrespective of the port.
• The small size and compact design of the E-Plane Tee is useful since it allows using this tee in microwave circuits that are largely affected by the dimensions of the device.
• E-Plane Tees are versatile since they can be used over a large frequency range.

Disadvantages of E-Plane Tee

Let us see some disadvantages of the E-Plane Tee

• Although E-Plane Tee provides isolation to some extent, it can’t provide much isolation. Other Tees like H-Plane Tee can offer more isolation between components minimizing the interaction.
• The temperature sensitivity of the E-Plane Tee is a major limitation of the E-Plane Tee since it can modify the electrical characteristic of the Tee with temperature variation. It can lead to inaccurate results.
• Sometimes E-Plane Tee can introduce polarization caused due to mode conversion by E-Plane Tee. This is majorly seen in rectangular configurations and can significantly alter the phase of the signal.
• E-Plane Tee can handle input power only to a certain range. In the case of high-power appliances, the Tee might suffer from significant damage which can cause permanent loss of the device.
• In case of high frequency, E-Plane Tee can cause high insertion loss. This can result in a loss of signal when the signal passes through the tee. Due to this other components are preferred over E-Plane Tee

Applications of E-Plane Tee

Let us see some applications of E-Plane Tee

• Microwave and RF systems use E-Plane Tee as power dividers. They can combine or split signals of microwave frequencies.
• Multiple antenna elements must be fed signals to ensure proper distribution. E-Plane Tees are used for these to form antenna-feeding networks.
• Due to their ability to control the amount of power being transferred, they can be used in filters that operate on microwave frequencies. They help to attain the specific characteristics of such filters.
• E-Plane Tees are largely used in directional couplers that are used to control the direction where the electromagnetic wave is being transmitted.
• E-Plane Tees can also be used to make other important devices like magic Tee which is a hybrid Tee made of E-Plane Tee and H-Plane Tee.

Conclusion

We have seen how E-Plane Tee can be a great means of splitting or combining the incoming waves because it shows the properties of both waveguides and Tees. We have seen the diagram of electric field distribution in E-Plane Tee and also seen how it operates in a circuit.

In addition to this, we have seen E-Plane Tee in Antenna Feed System and various other networks. Despite the multiple features offered by E-Plane Tee, it has certain limitations like a reflection of the signal. Some frequently asked questions have been answered which can be referred to in case of any doubts.

E-Plane Tee – FAQs

Why is E-Plane Tee called Series Tee?

The E-Plane Tee is called Series Tee because of its configuration. The side arm is parallel to the electric field and in series with each other giving it the name “series” Tee.

What is the difference between E-Plane and H-Plane Tee?

The main difference between E-Plane and H-Plane Tee is the difference in their configuration and direction of the dominant electric field component. In E-plane tee, the electric field vector is parallel to the plane of the junction, and in H-plane tee, the magnetic field vector is parallel to the plane of the junction.

What is a magic Tee?

A magic tee is also known as a hybrid Tee and is a four-port junction. It is a combination of E-Plane Tee and H-Plane Tee and provides combined features of the two Tees.