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Ku-Band Waveguide Filter

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 [1].  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.

Figure 1: FEKO model of Ku-band waveguide filter
filter3DView_6_0.png

 

 

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
(a) FEKO (b) Reference result [1]
S_param_6_0.png reference_result.jpg

 

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
(a) Real field component (b) Imaginary field component
near_field_real.png
near_field_imaginary.png

 

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.

Figure 4: Magnitude of Ey component near filter ports
near_field_E_y.png

 

 

References

[1] 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.