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Asymmetrical Capacitive Iris in Rectangular Waveguide (TE10): CAPIRIS_TE10

Symbol

Summary

CAPIRIS_TE10 models the behavior of asymmetrical infinitely thin capacitive iris (diaphragm) in rectangular waveguide. This iris is 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 discontinuity have the same size and are filled with air (only).

Topology

Figure 1. Dimensions of Capacitive Iris

Parameters

Name Description Unit Type Default
Wa Width of rectangular waveguide Length 22.86 mm
Wb Height of rectangular waveguide Length 10.16 mm
Yd1 Distance from lower edge of iris slot to waveguide bottom Length 4.08 mm
Yd2 Distance from upper edge of iris slot to waveguide bottom Length 6.08 mm
*ZCalc Switch - selector of TE10 characteristic impedance definition ("Power-Voltage"/"Voltage-Current"/"Normalized")   Power-Voltage

* indicates a secondary parameter

Parameter Details

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 [2] 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 operational frequency range.

Implementation Details

  1. CAPIRIS_TE10 evaluates the discontinuity impact using equivalent circuit parameters represented by quasi-static approximations given in [1] - [3].

  2. CAPIRIS_TE10 implementation assumes that rectangular waveguide is air-filled.

  3. When operational frequency is below cutoff or exceeds the upper frequency limit acceptable for this model, an appropriate warning is issued.

  4. Note that CAPIRIS_TE10 treats symmetrical iris as a special case of asymmetrical and uses different sets of quasi-static approximations for asymmetrical and symmetrical iris configurations. These sets of approximations have different frequency ranges where approximations are valid. The frequency range of validity for asymmetrical iris is narrower than the validity range for symmetrical iris. Let us denote Iris slot center as located at distance Yc = (Yd1 + Yd2)/2 from waveguide bottom (see Figure 1 in the "Topology" section ) and denote position of waveguide centerline as Yc= Wb/2. If Yc is nearby Yw (namely, 0.9*Yw < Yc < 1.1*Yw), this model treats iris as symmetrical and applies an extended frequency validity range.

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 CAPIRIS_TE10 (for example, filters), 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 an RWGT_TEmn model (m=1, n=0).

This model is developed to work in a frequency range when only dominant TE10 propagates.

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

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

References

[1] Gupta K.C. et al. "Computer-Aided Design of Microwave Circuits", Artech House, Mass., 1981, sec. 5.3.1.

[2] Marcuvitz N. "Waveguide Handbook", London, IEE, 1986 (first ed. 1951), Sec. 5.1, p. 268-269.

[3] Lewin L. "Theory of waveguides", London, Newness-Butterworths, 1975, Sec. 6.1.4.

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