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Waveguide Applications of FEKO


Magic tee waveguide coupler with delta port driven


The various CEM methods in FEKO make it well suited to the simulation of non-radiating structures. Waveguide circuits are an excellent example of this kind of problem and this application note highlights some of the benchmark simulations of waveguide components that have been done with FEKO.

Waveguide Magic Tee Coupler

The magic tee is a four-port, 180° hybrid splitter and like all of the coupler and splitter structures, the magic tee can be used as a power combiner or a divider.  It is ideally lossless, so that all power injected in to the sigma or delta port can be assumed to exit the remaining ports, without ohmic or other losses detracting energy.  A FEKO model of a WR-90 waveguide magic tee was simulated in FEKO while driving the sigma port with a waveguide source. The vector arrows indicate that the fields at the output ports are indeed in phase.

Dual-Mode Waveguide Cavity Filter

Waveguide filters come in a wide variety of designs. Guglielmi et al [1] published a design for a cavity based Ku-band dual-mode waveguide filter. This filter has a pass-band of approximately 11.0 to 11.2 GHz, with input reflections (S11) around –20 dB in this band. The transmission zeros on either side of the pass-band are also clearly visible in the computed response. Electric near-fields in the cavities were calculated at the 11.1 GHz resonant frequency and are shown below.

FEKO computed frequency response of Guglielmi et al's dual-mode waveguide filter



near_field_real_6_0.png near_field_imaginary_6_0.png
FEKO model of a dual-mode
waveguide filter

Real Imaginary

Ez field components inside the dual-mode waveguide filter at 11.1 GHz



Waveguide filter with dielectric blocks

Dielectrically Loaded Waveguide Filter

Shigesawa et al. [2] describe an evanescent-mode waveguide filter with dielectric blocks forming two parallel cut-off waveguide paths. The proposed filter is modelled in FEKO with the Finite Element Method (FEM) and driven with a FEM modal port. FEKO automatically computes the dominant mode for this port and uses this mode to excite the filter. Figure 5 shows a lateral cut-plane view of the model with metallic elements in orange and dielectric blocks in blue. As this filter is designed for a wide band of frequencies, FEKO's Adaptive Frequency Sampling (AFS) technology is applied to effectively select the minimum number of frequency points that will accurately characterise the filter's response.

S-parameter pass-band of waveguide filter with dielectric blocks



  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.

[2]   H. Shigesawa, M. Tsuji, T. Nkao, K. Takiyama, "Two-Path Cutoff Waveguide Dielectric Resonator Filters," IEEE Transactions on Microwave Theory and Techniques, Vol. 37, No. 7, July 1989, pp. 1105 - 1112.