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Symmetrical Inductive Iris (TE10): RWGIRIS_TE10

Symbol

Summary

RWGIRIS_TE10 models the behavior of a thick, perfectly conducting, dielectric-filled symmetrical, inductive diaphragm (metallic iris with internal edges parallel to vector E of a TE10 waveguide mode) represented as a discontinuity in a transmission line equivalent to the TE10 mode propagating in a rectangular waveguide. This model assumes that rectangular waveguides on both sides of the diaphragm have the same size and are filled with the same dielectric.

Parameters

Name Description Unit Type Default
Wa Width of rectangular waveguide Length 22.86 mm
Wb Height of rectangular waveguide Length 10.16 mm
IW Width of iris aperture (window) Length 5 mm
IT Thickness of iris wall Length 1.5 mm
M Number of higher order modes accounted for discontinuity modeling   10
Er Relative dielectric constant of dielectric filling the waveguide   1
Tand Loss tangent of dielectric filling the waveguide   0
*Mur Relative permeability of dielectric filling the waveguide   1
*Tanm Magnetic loss tangent of dielectric filling the waveguide   0
*Sigma Bulk conductivity of dielectric filling the waveguide Siemens/m 0
*ZCalc Switch - selector of TE10 characteristic impedance definition ("Power-Voltage"/"Voltage-Current"/"Normalized")   Power-Voltage

* indicates a secondary parameter

Parameter Details

M. Sets the number of higher modes that the model uses for series expansions representing fields on the diaphragm window.

Er, Tand, Mur, Tanm, Sigma. The material properties of the media filling the waveguide. These parameters are not used in the evaluation of discontinuity properties; they are used only for calculation of the denormalizing characteristic impedance of a rectangular waveguide.

Zcalc. Allows you to select a definition of the characteristic impedance of the TE10 mode propagating in a rectangular waveguide with Wa x Wb dimensions. Options include "Power-Voltage" ,"Voltage-Current", and "Normalized." This model uses the value of characteristic impedance to denormalize the computed normalized y-matrix of the modeled discontinuity. This selection must match the selection of the same parameter in the RWG_TEmn and RWGT_TEmn elements used in the same schematic.

The characteristic impedance definitions [1] are:

Here, fc is the cutoff frequency for TE10 and f is the operational frequency; η is the wave impedance of the open space filled with the waveguide dielectric.

ZNormalized=1

Parameter Restrictions and Recommendations

  1. The values of Wa and Wb must provide propagation of the single mode TE10 within the evaluation frequency range.

  2. The IT diaphragm thickness must be greater than zero.

  3. The IW width must be greater or less than Wa.

  4. The number of discontinuity modes M should be at least 10. You can experiment and determine a value of M large enough (for example, M=M1) to provide stable results for all the values M>M1.

    NOTE: A very thin diaphragm (large Wa/IT value) may demand a notable increase in the number of number of discontinuity nodes M (for example, M≥50). Insufficient M may cause inadequate approximation of the electromagnetic field at the iris aperture and be a source of unexpected issues.

Implementation Details

This model implies that a diaphragm is placed between the two segments of identical rectangular waveguides that support the dominant mode TE10. A mode-matching method [1] is applied to evaluate the scattering properties of two-width steps separated by a short waveguide of length equal to the diaphragm thickness.

Layout

This element does not have an assigned layout cell. You can assign artwork cells to any element. See “Assigning Artwork Cells to Layout of Schematic Elements” for details.

Recommendations for Use

To obtain the best results in simulated application based on RWGIRIS_TE10 (filters etc.), you should use the matching termination provided by the RWGT_TEmn model. For this purpose, terminate the application with the PORT_TN port model. PORT_TN should refer to a subcircuit that contains a RWGT_TEmn model (m=1, n=0).

NOTE: The implementation of this model relies on the involved numerical algorithm. Large values of the M parameter (above 10-15) may result in an extended execution time.

This model is developed to work in a frequency range when only dominant TE10 propagates. It provides reasonable results out of this range, but in this case user discretion is advised.

Normalized characteristic impedance implies that waveguide mode is propagating. This means: Never set ZCalc to "Normalized" if your operational frequency gets into below-cutoff region.

Note that the results depend on the selected definition of a waveguide characteristic impedance.

References

[1] K. C. Gupta, Ramesh Garg, Rakesh Chadha, Computer Aided Design of Microwave Circuits, Artech House, Mass., 1981.

[2] Tatsuo Itoh (Editor), Numerical Techniques for Millimeter-Wave Passive Structures, Chapter 9, John Wiley & Sons, New York, 1989.

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