Agilent Measurement Journal - Issue 4 - 2008 - (Page 40)

Table 1. The beneﬁts of each calibration technique can help determine which one is best for a particular application. Calibration techniques SOLT family SOLT ﬁ xed load (also known as two one-port + thru) SOLT sliding load Description Short, open, load, thru using a ﬁ xed impedance (usually 50 or 75 W) broadband load. Short, open, load, thru using a ﬁ xed impedance (usually 50 or 75 W) sliding broadband load. Key beneﬁts Widely used and understood. Applicable in nearly all cases. Requires well-deﬁned standards. Widely used and understood. Applicable in nearly all cases. Requires well-deﬁned standards.Higher accuracy due to better characterization of coupler directivity. More accurate at higher frequencies than a ﬁ xed load. Ideal for speciﬁc applications such as waveguide calibration. Ideal for setups such as: • noninsertable • multiport • physically long devices where cables should not be moved after calibration Ideal for multiport setups in which a minimum set of connections and disconnections are selected to optimize calibration. The more ports, the greater the time savings. Good choices for calibrating inside ﬁ xtures or on-wafer probing. Steps vary depending on available standards (e.g., TRL requires one line with ﬁnite length; LRL requires two lines, each with a different ﬁnite length). SOLT offset1 SOLR Offset short, open, load, with thru Short, open, load, reciprocal-thru (also called “unknown thru”) QSOLT Quick SOLT TRL family2 TRL TRM LRL LRM LRM+ ECal Modules ECal: Available as two- or four-port modules in various frequency ranges Thru, reﬂect, line Thru, reﬂect, match Line, reﬂect, line Line, reﬂect, match Line, reﬂect, offset match (called “LRM-plus”) Uses predeﬁned impedance states compared to measured values. USB controlled. Fast and repeatable. Ideal choice for eliminating human errors during calibration. Can be as accurate as SOLT sliding load manual calibration. 1. Different types of offset calibration standards are available and may or may not be covered here. For more information, refer to Reference 2. 2. TRL is not applicable for one-port calibration. The SOLT calibration method utilizes a 12-term error-correction model. The 12 terms refer to six error terms each in the forward and reverse direction through the DUT. Figure 2 shows the forward-direction error terms: ED (directivity), ES (source match), EL (load match), ERF (reﬂection tracking), E TF (transmission tracking) and E X (crosstalk). When performed properly, this method makes it possible to measure hundredths of a decibel of magnitude and millidegrees of phase. SOLT calibration standards are contained in widely available calibration kits that include a variety of connector types. They are relatively inexpensive and can last for years with proper care. Some SOLT calibration kits contain sliding loads, which make it possible to vary the line length of the path while maintaining a constant load impedance (usually 50 or 75 W). This is especially important at higher frequencies where good ﬁxed loads are difﬁcult to implement. The change in line length is directly proportional to a change in electrical length, which causes a phase shift in the measurement path. By using several different lengths with corresponding phase shifts during calibration, directivity of the network analyzer can more accurately measured (Figure 3). 40 Agilent Measurement Journal

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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