Agilent Technologies 8510 manual Fixed or sliding, Terminal impedance, Offset delay

The inductance as a function of frequency can be modeled by specifying the coefficients of a third- order polynomial (L0 + L1 x f + L2 x f2 + L3 x f3), with units of L0(nH), L1(10-24H/Hz),

L2(10-33H/Hz2) and L3(10-42H/Hz3).

For the waveguide example, the inductance of the offset short circuits is negligible. L0 through L3 are set equal to zero.

Fixed or sliding

If the standard type is specified to be a load or an arbitrary impedance, then it must be specified as fixed or sliding. Selection of “sliding” provides a sub-menu in the calibration sequence for multiple slide positions and measurement. This enables cal- culation of the directivity vector by mathematically eliminating the response due to a non-ideal termi- nal impedance. A further explanation of this tech- nique is found in the Measurement Calibration section in the Agilent 8510 Operating and Programming manual.

The load standard #4 in the WR-62 waveguide cali- bration kit is defined as a fixed load. Enter FIXED in the table.

Terminal impedance

Terminal impedance is only specified for “arbitrary impedance” standards. This allows definition of only the real part of the terminating impedance in ohms. Selection as the standard type “short,” “open,” or “load” automatically assigns the termi- nal impedance to be 0, ∞ or 50 ohms respectively.

The WR-62 waveguide calibration kit example does not contain an arbitrary impedance standard.

Offset delay

If the standard has electrical length (relative to the calibration plane), a standard is specified to have an offset delay. Offset delay is entered as the one- way travel time through an offset that can be obtained from the physical length using propaga- tion velocity of light in free space and the appro- priate permittivity constant. The effective propagation velocity equals √cεr . See Appendix B for a further description of physical offset lengths for sexed connector types.

Delay (seconds) =	√	εr
	c

= precise measurement of offset length in meters εr = relative permittivity (= 1.000649 for coaxial

airline or air-filled waveguide in standard lab conditions)

c = 2.997925 x 108 m/s

In coaxial transmission line, group delay is con- stant over frequency. In waveguide however, group velocity does vary with frequency due to disper- sion as a function of the cut-off frequency.

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