n blocks are limits of uncertainty (±) associated with measurements. etermination of complex impedance, it is necessary to measure not VSWR of the unknown, but also the phase of the unknown with respect ned plane of reference. The resulting data can then be used for ng the impedance of the unknown by means of a Smith chart or by ons using the following equations: & = distance between voltage minimum and point where load is considered to be located Part 1, Section 200.103 (c) and (d), also Section 200.109 (d). sentative for purposes of indicating uncertainties associated with calibrations of this type. The uncertainties indicated by the chart apply only, when the item calibrated is equipped with precision coaxial connectors. Larger uncertainties are given when non-precision connectors are involved [1]. The calibration services usually apply to standard terminations and mismatches or to sections of precision coaxial air-dielectric transmission line to ascertain electrical length. Calibration results are normally reported in terms of VSWR (referenced to 50 ohms) and phase angle. Other parameters such as impedance magnitude or electrical length in terms of linear dimensions can be provided if specified by the customer. Where the reflection coefficient, |T|, is required it may be readily obtained from the expression: [1] R. L. Jesch and R. M. Jickling, Impedance measurements in coaxial waveguide systems, Proc. IEEE, Vol. 55, No. 6, June 1967, 912-923. rvice is available only for terminations equipped with 14-mm on coaxial connectors,(b) and is available only at the frequencies ed in the table. The service provides for those cases where the inties resulting from lower cost slotted-line measurements (Page 7.34) acceptable. However, this particular reflectometer arrangement - yield phase information. n the reflectometer used in providing these services is composed y of coaxial elements, the theory of operation is the same as for lar waveguide reflectometers. The reference gives detailed theory ormation pertaining to reflectometer measurements. ce J. Anson, A guide to the use of the modified reflectometer technique VSWR measurement, J. Res. NBS, Vol. 65C, No. 4, Oct.-Dec. 1961, 217-223. e Part 1, Section 200.103 (c) and (d), also Section 200.109 (d). e Page 7.12. For waveguide reflectors having reflection coefficient magnitudes in the range 0.024 to 0.2, the estimated limits of uncertainty are (0.0002 + 0.002 |T|), where || is the numerical value of the reflection coefficient magnitude. For measurement of waveguide reflectors in WR42 waveguide (18.0-26.5 GHz) only, the estimated limits of uncertainty are: (A) (0.0004 + 0.0017 |г|) for the round flange-type connector and (B) ± (0.0008 + 0.0017 |г) for the square flange-type connector. General The reflectors must be fitted with standard waveguide flange-type connectors. The face of these flanges should be machined flat and smooth and should not contain protrusions or indentations. Considerable care must be exercised in keeping the mating connector flange surfaces smooth and clean. Accurate alignment of the interior surfaces of the joining waveguides at the flange junction also is very important. The back of the flange which makes contact with the connecting bolts should be nominally flat and free of soft materials including paint. The connecting holes of the flange should be symmetrically and accurately aligned to the rectangular waveguide opening. Reference [1] W. J. Anson, A guide to the use of the modified reflectometer technique of VSWR measurement, J. Res. NBS, Vol. 65C, No. 4, Oct.-Dec. 1961, 217-223. The measurement technique utilized in reflection measurements is described in this paper. (b) See Part 1, Section 200.103 (c) and (d), also Section 200.109 (d). OF NONREFLECTING WAVEGUIDE PORTS Schedule Movable ecting waveguide ports can be measured with estimated limits of inty of (0.00013+ 0.0032 |r|), where || is the numerical value reflection coefficient magnitude. The present reflection calibration can be used to measure reflection coefficient magnitudes as small as with the above uncertainty. luation of nonreflecting waveguide ports in WR42 waveguide (18.0z) only, the estimated limits of uncertainty are: (0.0004 0.0032 |T) for the round flange-type connector n nonreflecting as used here indicates that the waveguide port has signed or adjusted with the intent to produce a reflection coefficient de, r, equal to zero. Although most waveguide ports for such tions cannot produce a reflection coefficient magnitude identically o zero, their reflection coefficient magnitudes often approach zero osely. Useful information is gained by evaluating the extent to which n be accomplished. so includes evaluation of matched loads. e Part 1, Section 200.103 (c) and (d), also Section 200.109 (d). |