Importance and estimation of mismatch uncertainty for RF parameters in calibration laboratories

Abstract

Abstract.A number of calibration techniques are used in Radio Frequency (RF) calibration for power, attenuation and impedance parameters. Mismatch uncertainty plays a major role in these measurements and in estimation of combined uncertainty according to ISO/IEC 17025:2005 and GUM document. Formulas to evaluate the mismatch uncertainty in terms of reflection coefficient, voltage standing wave ratio and scattering parameters have been evaluated earlier and are being used in RF calibration. The present paper summarizes the mismatch formulas previously studied and the modified ones suitable to the measurement system and techniques available today. For power and attenuation calibration in the particular frequency range, an establishment of traceability for one-port measurement in the same frequency range is required. The methods to reduce and control this uncertainty component and their limitations are also discussed for best measurements practices in the calibration laboratories.

Experimental estimation of mismatch uncertainty in radio – frequency power and attenuation measurements

“…M1110 is taken as a DUT and its reflection coefficient values (Γ DUT ) are measured using VNA. These measured values along with their associated uncertainties from VNA and source reflection coefficient (Γ G ) of 0.231 (VSWR ≈ 1.6) have been applied in equation (1) to estimate the mismatch uncertainties [7]. The mismatch uncertainty calculated using equations (2) and ( the same range of frequencies.…”

“…For a fixed attenuator (<10 dB), when only magnitude is known (linear), total uncertainty contribution MA T due to mismatch error is given by [7]:…”

“…In Intermediate frequency (IF) substitution technique for attenuation measurement, the mismatch uncertainty in terms of VSWR values is expressed by [7],…”

“…The expression for the mismatch uncertainty for null comparison power measurement MNP Γ has modified at 50 MHz (f 1 ) and the measurement frequency (f 2 ) and given as [7],…”

“…So, the user is spending more time in searching and implementing the best formula depending on the parameter being measured, Correspondence: kpatel@south.du.ac.in input parameters, measurement setup, type of representations, complex or linear etc. An effort was made to address this issue for RF engineers, the formulas have been presented with the sufficient references to give a glimpse of their appropriate and suitable applications at a single place [7]. However, further work was required in this area, first to study the response of the equations available in different linear and complex representations of input quantities.…”