**Subject :**Microwave Engineering

## E-plane tee (series tee)

An E -plane tee is a waveguide tee in which the axis of its side arm is parallel to the E field of the main guide (see Fig. 1). If the collinear arms are symmetric about the side arm, there are two different transmission characteristics (see Fig. 2). It can be seen from Fig. 1 that if the E-plane tee is perfectly matched with the aid of screw tuners or inductive or capacitive windows at the junction, the diagonal components of the scattering matrix, S11, S22, and S33, are zero because there will be no reflection. When the waves are fed into the side arm (port 3), the waves appearing at port 1 and port 2 of the collinear arm will be in opposite phase and in the same magnitude. Therefore :

..(1)

is always negative. The negative sign merely means that SI3 and S23 have opposite signs. For a matched junction, the S matrix is given by

**Figure 1: E-plane tee
**

**Figure 2: Two-waytransmissionof E-plane tee (a) Input through main arm (b) Input from side arm**

...(2)

From the symmetry property of S matrix, the symmetric terms in Eq. (2) are equal and they are

...(3)

From the zero property of S matrix, the sum of the products of each term of any column (or row) multiplied by the complex conjugate of the corresponding terms of any other column (or row) is zero and it is :

...(4)

Hence :

...(5)

This means that either SI3 or Sf3, or both, should be zero. However, from the unity property of S matrix, the sum of the products of each term of anyone row (or column) multiplied by its complex conjugate is unity; that is:

..(6)