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Agilent Specifying Calibration Standards for the Agilent 8510 Network Analyzer Product Note 8510-5B.
2 3 3 3 4 5 5 7 7 8 9 9 9 11 12 12 12 14 14 15 16 16 17 17 17 18 18 18 18 19 19 19 19 19 20 20 20 21 21 22 22 22 23 23 26 29 Introduction Measurement errors Measurement calibration Calibration kit Sta.
3 Introduction This pr oduct note co vers measurement calibration requirements f or the Agilent 8510B/C network analyzer . All of t he capabilities described in this note also apply to the A gilent 85.
4 The arra y coeff icients are computed by measuring a set of “kno wn” devices connected at a fixed point and sol ving as the vector difference between the modeled and measured response. The full 2-por t er r or model sho wn in Figure 1 is an exam ple of only one of the measurement calibra- tions a vailable with the 8510.
5 Standard definition Standard definition is t he process of mathematical- ly modeling the electrical charact eristics (delay , attenuation and impedance) of each calibration standard.
6 T able 1. Standard definitions table T able 2. Standard class assignments.
7 Modification procedure Calibration kit modif ication pro vides the capability to adapt t o measurement calibrations in other con- nector types or to generate more precise error models fr om existing kits.
8 Define standards A glossar y of standard definition parameters used with the Agilent 8510 is included in this section. Each parameter is described and appropriate con- versions are listed f or im plement ation with t he 8510. T o illustrate, a calibration kit f or WR-62 rec- tangular wav eguide (operating frequency range 12.
9 Each standard is described using the Standard Definition Table in accordance wit h t he 1- or 2- port model. The St andard Definition t able for a wav eguide calibration kit is sho wn in Table 1. Each standard type (shor t, open, load, thru, and arbi- trar y impedance) ma y be def ined by the parame- ters as specif ied below .
10 It is not possible t o remov e fringing capacit ance, but the result ant phase shif t can be modeled as a function of frequency using C 0 t hr ough C 3 (C 0 +C l f + C 2 f 2 + C 3 f 3 ,.
11 Note In some cases (when t he phase response is linear with respect t o frequency) the response of an open can be modeled as an equivalent “increment al” length. This method will serve as a f irst order appro xima- tion onl y , but can be useful when data or st an- dards for t he abov e modeling techniques are not available.
The inductance as a function of frequency can be modeled b y specifying t he coef ficients of a third- order polynomial (L 0 + L 1 f + L 2 f 2 + L 3 f 3 ), with units of L 0 (nH), L 1 (10 -24 H/Hz), L 2 (10 -33 H/Hz 2 ) and L 3 (10 -42 H/Hz 3 ).
13 The conv ention f or definition of offset dela y in wav eguide requires entr y of t he delay assuming no dispersion. F or wa veguide transmission line, the Agilent 8510 calculat es t he ef f ects o.
14 µ r = relativ e permeability constant of t he medium (equal to 1.0 in air) ε r = relativ e permittivity constant of t he medium (equal to 1.000649 in air) D = inside diameter of outer conductor d.
15 Therefore, for the WR -62 wav eguide standard defi- nition table, offset loss of zero ohm/sec is entered for all f our standards. Lower/minimum frequency Lo wer frequency defines the minimum frequency at which the st andard is to be used f or the purposes of calibration.
16 Upper/maximum frequency This specifies the maximum frequency at which the standard is valid. In broadband applications, a set of banded standards ma y be necessar y to pr o- vide constant response. For example, coaxial offset standards (i.e., 1 / 4 λ offset short) are generally spec- ified o ver bandwidths of an octav e or less.
17 Note Mathematical operations on measurements (and display ed data) after calibration are not corrected for dispersion. Enter W A VEGUIDE int o t he st andar d definition table for all f our standards. Standard labels Labels are entered through the title menu and may contain up to 10 characters.
18 S 11 A,B,C and S 22 A,B,C S 11 A, B,C and S 22 A,B,C cor respond to the S 11 and S 22 ref lection calibrations for por t 1 and port 2 respectivel y. These three classes are used by the Agilent 8510 t o solve for t he systematic errors; directivity , source mat ch, and ref lection tracking.
19 TRL Thru TRL Thru corresponds t o t he measurement of t he S-parameters of a zero-length or shor t t hru connec- tion betw een port 1 and por t 2. The Thr u, Ref lect and Line classes are used ex clusively for t he t hree steps of t he TRL 2-PORT calibration.
20 Each adapter is specified as a sing le delay/thru standard and up to sev en standards numbers can be specified into t he adapt er class. Standard Class labels Standard Class labels are entered t o facilit ate menu-driven calibration.
21 Again, cal kit labels should be chosen t o best describe the calibration devices. The “B.1” default suff ix cor responds t o the kit’s mechanical revision (B) and mathematical revision (1).
22 User modified cal kits and Agilent 8510 specifications As noted previously , the resultant accuracy of the 8510 when used with an y calibration kit is depend- ent on how well its standards are def ined and is verified through measurement of a device wit h traceable frequency response.
23 Appendix A Calibration kit entry procedure Calibration kit specif ications can be ent ered into the Agilent 8510 using the 8510 disk drive, a disk drive connected to the system bus, by front panel entr y , or t hr ough program contr ol by an external controller .
24 Front panel procedure: (P -band waveguide example) 1. Prior to modifying or generating a cal kit, store one or both of the cal kits in t he 8510’s non- volatile memor y t o a disk. 2. Select CAL menu, MORE. 3. Prepare to modify cal kit 2: press MODIFY 2.
25 4. Change the class label for S 11 A: L ABEL CL ASS, S 11 A, ERASE TITLE. 5. Enter t he label of PSHORT 1 b y using the knob, the SELECT sof t key and the SP A CE soft ke y.
26 Appendix B Dimensional considerations in coaxial connectors This appendix describes dimensional considera- tions and required conv entions used in deter min- ing the physical offset lengt h of calibration standards in sexed coaxial connector families.
27 Female type-N Male type-N 7 mm Coaxial connector T ype-N coaxial connector interface The location of the “calibration plane” in T ype-N standards is the outer conductor mating surfaces as shown below . Note: 1.0mm, 1.85mm and 2.4mm connectors not shown, but similar to 3.
28.
29 Appendix C Cal coefficients model Offset devices like of fset shor ts and offset opens can be modeled by t he follo wing signal f low g raph : Figure 1 Signal flow graph model of offset devices The offset portion of t he open or shor t, is modeled as a per f ectly unif orm lossy air dielectric transmis- sion line.
30 Their first or der appro ximations, R is small and G=0, are: Equation 3 Since Equation 4 F or coaxial devices.
31 then: Equation 5 Equation 6 If the Of fset delay=0, then t he coef ficient of ref lection, Γ = Γ L ..
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