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What are the calibration kit coefficients?

The open, short and load standards in the calibration kit must all have a mathematical model of them. For the load this is very simple - a 50 Ω resistor is assumed. The load must be a high quality, having a high return loss throughout the frequency range of the kit.

The opens and shorts are quite different. Each will be considered to have a transmission line will have some length L, typically of the order of a few mm, which causes a delay dT typically of the order of a few 10s of ps. A short will be terminated in an inductor, although the inductance of that is usually negligible. The open will be terminated in a capacitance due to the fringe capacitance, of the order of 100 fF. This fringe capacitance can not be ignored, and neither can it be considered independent of frequency. The capacitance is normally represented by a 3rd order polynomial as a function of frequency. HP, Agilent, Anritsu, Keysight and Copper Mountain all use the following definition

Cfringing=C0x10-15 + C1x10-27f + C2x10-36f2+C3x10-45f3

Rohde and Schwarz, Anritsu don't specify a delay of the standard, but a length. Care needs to be taken to be sure the units are correct. One of Kirkby Microwave's customers assumed the VNA wanted an offset length in mm, whereas actually the VNA was expecting the value in metres. Needless to say, having a coefficient 1000x wrong caused problems. The following are a set of typical coefficients for one of our SMA calibration kits. Since the end of 2017, kits have individually measured parameters, but for earlier kits, the following will apply.

System Zo = 50 Ω         Calibration kit label: 85033
Type C0 C1 C2 C3 Fixed or sliding Delay(ps) Zo(Ω) Loss(G Ω/s) Fmin (GHz) Fmax (GHz) Coax or waveguide Standard
Female short           41.398 50 3.0 0 999 Coax SHORT(M)
Female open 53.004 135.167 95.6305 30.937   39.8 50 3.0 0 999 Coax OPEN(M)
Load         Fixed 0 50 3.0 0 999 Coax Broadband
Delay/thru           0 50 3.0 0 999 Coax Thru
Male short           57.834 50 3.0 0 999 Coax SHORT(F)
Male open 50.389 761.36 -968.22 68.376   55.1 50 3.0 0 999 Coax OPEN(F)


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