Z0 = | 1 |
|
| In( | D | ) = 59.9585 | r | In( | D | ) |
2π |
| ε | d | εr | d |
∝r = relative permeability constant of the medium (equal to 1.0 in air)
εr = relative permittivity constant of the medium (equal to 1.000649 in air)
D = inside diameter of outer conductor d = outside diameter of inner conductor
The 8510 requires that the characteristic imped- ance of waveguide transmission line is assigned to be equal to the SET Z0.
The characteristic impedance of other transmis- sion media is not as easily determined through mechanical dimensions. Waveguide impedance, for example, varies as a function of frequency. In such cases, normalized impedance measurements are typically made. When calibrating in waveguide, the impedance of a “matched” load is used as the impedance reference. The impedance of this load is matched that of the waveguide across frequency. Normalized impedance is achieved by entering SET Z0 and OFFSET Z0 to 1 ohm for each standard.
Offset Z0 equal to system Z0 (SET Z0) is the assigned convention in the 8510 for matched wave- guide impedance.
Offset loss
Offset loss is used to model the magnitude loss due to skin effect of offset coaxial type standards only. The value of loss is entered into the standard defi- nition table as gigohms/second or ohms/nanosec- ond at 1 GHz.
The offset loss in gigohms/second can be calculat- ed from the measured loss at 1 GHz and the physi- cal length of the particular standard by the following equation.
Offset loss ( |
| GΩ | ) |
|
| = | dBloss | 1 GHz C Z0 |
|
|
|
|
| ||||||
| s |
| 1 GHz | 10 loge(10) | r | ||||
|
|
|
|
| |||||
where:
dBlOSS 1 GHz =measured insertion loss at 1 GHz Z0 = offset Z0
= physical length of the offset
The 8510 calculates the skin loss as a function of frequency as follows:
Offset loss |
|
| GΩ |
| = Offset loss |
|
| GΩ |
|
| f(GHz) | |
( | s ) | ( | s ) | 1GHz X | ||||||||
|
|
| ||||||||||
Note: For additional information refer to Appendix C.
For all offset standards, including shorts or opens, enter the one way skin loss. The offset loss in waveguide should always be assigned zero ohms by the 8510.
14
