Agilent Measurement Journal - Issue 4 - 2008 - (Page 43)

Table 2. This comparison of calibration types, tradeoffs and accuracies can help identify which one is best for a particular application. The ratings are low (L), medium (M) and high (H). Tradeoffs Calibration techniques Cost SOLT family1 SOLT fixed load SOLT sliding load SOLT offset2 SOLR (unknown thru) QSOLT TRL family5 TRL TRM LRL LRM ECal modules ECal: Available as twoor four-port modules L M-H M-H One-port calibration Repeatability Skill level H M L-H L M L-H Not applicable Accuracy L-M (10-1%) M-H (2-0.3%) M-H (1-0.2%) Cost L-H M-H M-H L-M L-H H L-M H+ H L-H (10-0.2%) M Two-port calibration Repeatability Skill level L-H M L-H M-H M-H M M-H L-M L-M H L-H M L-H L-M M-H H L-M H+ H L Accuracy L-H (10-0.5%) M-H (5-0.3%) M-H (3-0.05%) L-H3 (10-0.5%) L-H4 H+ (<1%) L-M (10-2%) L-M (<3%) L-M (12-2%) L-H (5-0.3%) Not applicable M H L 1. The thru (T) standard is applicable only with two-port calibration. 2. Different types of offset calibration standards are available and may or may not be covered here. For more information, refer to Reference 2. 3. Because SOLR eliminates the need for adapters during calibration (along with their associated uncertainties), it may exceed the accuracy of SOLT. 4. Accuracy of QSOLT depends on the quality of the calibration and the accuracy of the reduction algorithm applied to the calibrated data. 5. TRL is not applicable to one-port calibration. to establish a baseline. A network analyzer’s deviation from a standard during calibration deﬁnes its accuracy. Put another way, any error introduced during calibration will directly affect the measurement accuracy of the network analyzer. It is essential to perform a proper calibration to ensure optimal measurement performance. The following key topics must be considered when using a network analyzer to ensure the best overall accuracy. To begin, recognize that the calibration of a network analyzer is a measurement: It requires the care and precision of any RF/microwave measurement. Considering mismatch measurement uncertainties Consider a circuit trace used to connect a network analyzer to a DUT with a 10 percent error in its characteristic impedance (e.g., 55 W with a 50-W network analyzer). A simple calculation yields a reﬂection coefﬁcient (r) for the source and load of 0.05, equal to a VSWR of 1:1.10.5 This results in a mismatch loss of 0.01 dB and mismatch uncertainty of ±0.02 dB. Now consider a circuit trace between the network analyzer and DUT with a reﬂection coefﬁcient of 0.13, equal to a VSWR of 1:1.30.5 This is well below a VSWR of 1:2.0, which is often speciﬁed in some commercial applications. In this case, the mismatch loss jumps to 0.075 dB, and mismatch uncertainty of ± 0.15 dB. Figure 5 illustrates this relationship. Reflection coefficient 0.00 3.00 2.00 Loss (dB) 1.00 1.04 1.08 1.13 1.17 1.22 VSWR 1.86 3.00 5.67 19.00 0.02 0.04 0.06 0.08 0.10 0.30 0.50 0.70 0.90 0.00 1.00 -1.00 -2.00 -3.00 Upper mismatch error (dB) Lower mismatch error (dB) Mismatch loss (dB) VSWR = (1+r)/(1–r) Maximum mismatch error limits (dB) = 20log10(1±|rsource rload|) Mismatch loss (dB) = -10log10(1–r2) where r = reflection coeficient and rsource = rload Figure 5. This graph shows the relationship between reﬂection coefﬁcient, mismatch loss and uncertainty. Agilent Measurement Journal 43

Table of Contents Feed for the Digital Edition of Agilent Measurement Journal - Issue 4 - 2008

Agilent Measurement Journal - Issue 4 - 2008 Delivering Confidence through Compliance with Standards Contents Emerging Innovations Trying Early Device Implementations at the IEEE 1588 PlugFest Achieving Greater Confidence in Measurement Accuracy through Consistency in Calibration Services Overcoming the Challenges of RFID Component Testing 3GPP LTE: Introducing Single- Carrier FDMA Ensuring Reliable Operation and Performance in Converged IP Networks Testing Storage Area Networks and Devices at 8.5-Gb/s Fibre Channel Rates Choosing an Appropriate Calibration Method for Vector Network Analysis Making Traceable EVM Measurements with Digital Oscilloscopes Exploring Terahertz Measurement, Imaging and Spectroscopy: The Electromagnetic Spectrum’s Final Frontier Interpreting Quoted Specifications when Selecting Digitizers

Agilent Measurement Journal - Issue 4 - 2008

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