Waveguide transmission lines are used in communications systems to feed horn or slotted waveguide antennas. Usually a filter is required to remove unwanted signal content and realising a filter in waveguide form is required to integrate it with the rest of the system. A design for a two-resonator waveguide filter for the Ku-band is given in [1]. Here such a filter is modeled in FEKO to determine the filter response.

Figure 1 shows the FEKO model for the filter and the waveguide ports are excited in the TE₁₀ mode. Notice the fine mesh near the corners of the waveguide discontinuities to account for a rapidly varying field in these regions.

Figure 1: FEKO model of Ku-band waveguide filter

An S-parameter calculation is performed and the results shown in Figure 2. The passband is roughly 11.0 ~ 11.2 GHz with reflections mostly below -20 dB in this band. Also clearly visible are the transmission zeros on either side of the pass band. Because the electric fields inside the structure are mainly y-directed electric symmetry exists in the xz-plane. By exploiting this symmetry computation time and memory requirements are greatly reduced. The frequency response shown in Figure 2 also shows the results obtained by using symmetry.

Figure 2: Frequency response of Ku-band waveguide filter

Electric near-fields are calculated in the resonating cavities at 11.1 GHz. A section in the xz-plane through the filter structure shows the E_y fields in Figure 3. Figure 3(a) shows the real field components and Figure 3(b) shows the imaginary field components.

Figure 3: Electric near-fields in resonating cavities at 11.1GHz
(a) Real field component (b) Imaginary field component

Finally the electric field is calculated on the inside of the two ports. Figure 4 shows the magnitude of the E_y field component for a TE₁₀ driving mode.

Figure 4: Magnitude of Ey component near filter ports

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