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A Ku-band waveguide filter is modelled in FEKO to determine its frequency response
Waveguide transmission lines are used in communications systems to feed horn or slotted waveguide antennas. A filter is usually 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 . Here such a filter is modelled in FEKO to determine the filter response.
Figure 1 shows the FEKO model for the filter where the FEM modal ports are excited with the fundamental mode. Notice the fine mesh near the corners of the waveguide discontinuities to account for a rapidly varying field in these regions.
An S-parameter calculation is performed and the results shown in Figure 2. The passband is 11.04 ~ 11.18 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 (a) depicts both FEM and MoM solutions to the problem.
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 xy-plane through the filter structure shows the Ez 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
Finally the electric field is calculated on the inside of the two ports. Figure 4 shows the magnitude of the Ez field component when the system is excited with the fundamental propagating mode.
 M. Guglielmi, P. Jarry, E. Kerherve, O. Roquebrun, D. Schmitt, “A New Family of All-Inductive Dual-Mode Filter”, IEEE Transactions on Microwave Theory and Techniques, Vol. 49, No. 10, Oct. 2001, pp. 1764-1769.
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