E-T waveguide power divider

This is a 2-way power divider I made, which is used in a broadband feed net of a horn antenna array. Firstly, a E-T junction (figure 1a) can equal to a transmission line model like figure 1b.The junction is inductive.Here we assume that the impedance of L1 is Z0. So the S11 of this structure is not very good. For a perfect power divider, the impedance of L2 and L3 must be 2Z0, at the same time, the junction must not be inductive nor capacitive.

Figure 1 normal E-T junction

For the impedance, we can reduce the height of the waveguide to increase the impedance, while we can add a step in the junction which is capacitive and it can neutralize the inductance. So the final structure of the E-T junction is like figure 2. Figure 3 shows the S11 of this structure, the cutoff frequency of the waveguide is about 10.5GHz.

Figure 2 broadband E-T junction

Figure 3 the S11 of the structure

Now the impedance of L2 and L3 is 2Z0. We can use the impedance conversion method to convert the impedance to Z0. In the figure 4, I use Chebyshev impedance conversion method. The length of each impedance transformation segment is λ/4. The S11 of this structure shown in figure 5.

Figure 4 2-way power divider with Chebyshev impedance conversion

Figure 5 the S11 of power divider with Chebyshev impedance conversion

The Corner of a Waveguide

Some simulation results of the 90 degrees corner of the waveguide with CST Mcirowave Studio.

There are two kinds of waveguide corner, one turns in E plane, the other turns in H plane.

Figure 1 is the model of the E plane waveguide corner. The size of the waveguide is 14.5mm x 9.525mm.

Figure 1. The model of the E plane waveguide corner

I set a variable r1 in the CST and watch the S11 when the variable changes. The r1 is the inner radius of the corner. See figure 2.

Figure 2. The inner radius of corner

I also compare the round corner with the triangular corner. The model of the triangular corner is shown in figure 3.

Figure 3. The E plane triangular waveguide corner

I use the parameters sweep function in the CST to simulate the S11 which is related to the radius r1. The frequency range is from 10GHz to 15GHz. The results of the simulation is in figure 4. The worst one is the triangular corner, the dash line. And the S11 will be better when r1 increases until r1 is larger than 8mm.

Figure 4. The S11 of the E plane corner

The results of the H plane waveguide corner is similar. The figure 5 is the model and figure 6 is the S11.

Figure 5. The model of the H plane waveguide corner

Figure 6. The S11 of the H plane corner