CSTEPIO is a closed form model of a double-step in inner and outer conductors. Both steps share the same cross-section and have a common reference plane. CSTEPIO allows a step in the dielectric constant at the same cross section. Step discontinuity is represented as shunt frequency-independent capacitance.

Name | Description | Unit Type | Default |
---|---|---|---|

Di1 | Diameter of inner conductor @ Node 1 | Length | 2.9027 mm |

Do1 | Diameter of outer conductor @ Node 1 | Length | 10.287 mm |

Di2 | Diameter of inner conductor @ Node 2 | Length | 2.9027 mm |

Do2 | Diameter of outer conductor @ Node 2 | Length | 10.287 mm |

Er1 | Relative dielectric constant filling the coaxial waveguide @ Node 1 | 1 | |

Er2 | Relative dielectric constant filling the coaxial waveguide @ Node 2 | 1 |

**Er1, Er2.** Dielectric constants of media filling the
coaxial waveguide at both sides of the reference plane (see "Topology").

CSTEPIO is implemented as a closed form approximation of total step capacitance based
on [1]. Note that [1] uses the results of a full solution ([2]) to obtain this
approximation. The absolute approximation error in capacitance (if
ε_{r1}=ε_{r2})can be estimated
(according to [1]) as 0.18(D_{i}+D_{o})pF where
D_{i} and D_{o} stand for averaged inner and
outer diameters (expressed in meters). If
ε_{r1}≠ε_{r2}, then the error
may increase because accounting for the inhomogeneous dielectric does not come from the
approximation of the full solution, but is rather based on phenomenologically justified
assumptions.

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.

CSTEPIO allows any combination of Di1, Do1, Di2, Do2, Er1, Er2. However, the best results are achieved if the following inequalities hold:

0.01<α<0.7

1.5<τ<6

For outer step α is
(D_{omin}-D_{i})/(D_{omax}-D_{i}).
Here D_{omin},D_{omax} stands for the smaller
and larger of the outer diameters and D_{i} stands for each of the
inner diameters. α should be tested for both D_{i}. The τ
variable should be evaluated and tested as
D_{omax}/D_{i} for both
D_{i}.

For the inner step, α is
(D_{o}-D_{imax})/(D_{omax}-D_{imin}).
Here D_{imin}, D_{imax} stands for the smaller
and larger of the inner diameters and D_{o} stands for each of the
outer diameters. α should be tested for both D_{o}. The τ
variable should be evaluated and tested as
D_{o}/D_{imin} for both
D_{o}.

This model implies that step capacitance is frequency-independent. According to [1],
step capacitance generally grows with frequency and deviates from static value at about
10% if the evaluation frequency exceeds 0.4 Fc, where Fc is the lower cutoff
frequency of mode TM_{01} for coaxial waveguides at nodes 1 and
2.

This lower cutoff frequency may be evaluated as the lower value

(where c in the nominator is the speed of light, ε stands for
dielectric constant, and D_{o},D_{i} are outer
and inner diameters) applied in turn to coaxial waveguides at node 1 and node 2.

**NOTE: **This model is developed to work in a frequency
range where only dominant TEM mode propagates.