---
title: "Short note: E-plane tee"
subject: "RF and Microwave Engineering"
chapter: 4
key: "semester_7/rf_and_microwave_engineering:eplane-tee-note"
source: https://www.bctengineer.com/q/semester_7/rf_and_microwave_engineering/eplane-tee-note
site: BCT Engineering
---

# Short note: E-plane tee

RF and Microwave Engineering · Chapter 4: RF and Microwave Components and Devices

- Asked in: 2080 Baisakh, 3 marks
- Video: [E Plane Tee (Basics, Working, Internal structure, S Matrix & Applications) Explained in Microwave](https://www.youtube.com/watch?v=5Q4TNOf1gMc) — Engineering Funda
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/rf_and_microwave_engineering/eplane-tee-note
- Whole chapter: https://www.bctengineer.com/md/semester_7/rf_and_microwave_engineering/chapter-4

## Question

Write a short note on E-plane tee.

## Short answer

E-plane tee is a series tee with side arm on the broad wall. Input at side arm splits equally to collinear arms 180 degrees out of phase; equal in-phase inputs cancel at side arm. Its S-matrix has 1/2 and 1/sqrt(2) entries.

## Answer

An **E-plane tee (series tee)** is a waveguide tee junction in which the side arm (port 3) is attached to the **broad wall** of the main guide, so the side arm axis is parallel to the E-field of the TE10 mode. Ports 1 and 2 are the collinear arms.

```text
          port 3 (E-arm)
             | |
   ----------+ +----------
 (1)                    (2)
   -----------------------
```

**Behaviour:**
- Input at port 3 divides equally into ports 1 and 2 **180° out of phase** (the E-field lines bend in opposite directions).
- Equal in-phase inputs at 1 and 2 cancel at port 3; anti-phase inputs add at port 3.
- It acts like a **series** connection of the side arm with the main line.

**S-matrix (lossless, side arm matched):**
```text
       |  1/2    1/2    1/√2 |
 [S] = |  1/2    1/2   -1/√2 |
       |  1/√2  -1/√2    0   |
```
**Uses:** power division with phase reversal, balanced mixers, impedance tuners (with a sliding short in port 3) and as part of a magic tee.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. The side arm of an E-plane tee is attached to
   A. the narrow wall, parallel to the H-field
   B. the broad wall, parallel to the E-field
   C. the end of the guide
   D. both walls
   Answer: B. That gives a series-type junction. (Key point: Side arm location)

2. Equal in-phase inputs at ports 1 and 2 of an E-plane tee
   A. add at port 3
   B. all go to port 1
   C. cancel at port 3
   D. are absorbed in the tee
   Answer: C. Port 3 is a difference port, so anti-phase inputs add there. (Key point: Phase behaviour)

3. An E-plane tee acts like a
   A. shunt connection
   B. parallel-plate capacitor
   C. circulator
   D. series connection of the side arm with the main line
   Answer: D. That is why it is called a series tee. (Key point: Connection type)

## Related in RF and Microwave Engineering

- [S-matrices of E-plane tee, H-plane tee and duplexer](https://www.bctengineer.com/question.md?key=semester_7%2Frf_and_microwave_engineering%3Aeplane-hplane-tee-duplexer-smatrix) — RF and Microwave Engineering, chapter 4
- [Short note: E-plane tee against H-plane tee](https://www.bctengineer.com/question.md?key=semester_7%2Frf_and_microwave_engineering%3Aeplane-vs-hplane-tee-note) — RF and Microwave Engineering, chapter 4