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Prof. David R. Jackson Dept. of ECE

ECE 5317-6351 Microwave Engineering. Fall 2011. Prof. David R. Jackson Dept. of ECE. Notes 16. S -Parameter Measurements. S-Parameter Measurements. S-parameters are typically measured, at microwave frequencies, with a network analyzer (NA).

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Prof. David R. Jackson Dept. of ECE

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  1. ECE 5317-6351 Microwave Engineering Fall 2011 Prof. David R. Jackson Dept. of ECE Notes 16 S-Parameter Measurements

  2. S-Parameter Measurements • S-parameters are typically measured, at microwave frequencies, with a network analyzer (NA). • These instruments have found wide, almost universal, application since the mid to late 1970’s. • Vector network analyzer: Magnitudes and phases of the S parameters are measured. • Scalar network analyzer: Only the magnitudes of the S-parameters is measured. • Most NA’s measure 2-port parameters. Some measure 4 and 6 ports.

  3. Vector Network Analyzer (VNA) Test cables Port 2 Port 1 DUT Hewlett-Packard 8510 DUT

  4. Network Analysis of VNA Measurement

  5. S-Parameter Measurements Error boxes contain effectsof test cables, connectors, couplers,…

  6. S-Parameter Measurements (cont.) This is called “de-embedding.”

  7. Calibration “Short, open, match” calibration procedure SC -1 OC +1 Z0 0 Connect short open match Calibration loads Recall from Notes 15:

  8. Calibration (cont.) “ Thru-Reflect-Line (TRL)” calibration procedure This is an improved calibration method that involves three types of connections: The “thru” connection, in which port 1 is directly connected to port 2. The “reflect” connection, in which a load with an (ideally) large (but not necessarily precisely known) reflection coefficient is connected. The “line” connection, in which a length of matched transmission line (with an unknown length) is connected between ports 1 and 2. The advantage of the TRL calibration is that is does not requires precise short, open, and matched loads. This method is discussed in the Pozar book (pp. 193-196).

  9. Z-Parameter Extraction Assume a reciprocal and symmetrical waveguide or transmission-line discontinuity. Examples Microstrip gap Waveguide post We want to find Z1and Z2 to model the discontinuity.

  10. Z-Parameter Extraction (cont.) Plane of symmetry (POS) POS

  11. Z-Parameter Extraction (cont.) Assume that we place a short or an open along the plane of symmetry.

  12. Z-Parameter Extraction (cont.) The short or open can be realized by using odd- or even-mode excitation. T Incident voltage waves - + Odd mode excitation + + Even mode excitation The even/odd-mode analysis is very useful in analyzing devices (e.g., using HFSS).

  13. De-embeding of a Line Length We wish the know the reflection coefficient of a device under test (DUT), but the DUT is not assessable directly – it has an extra length of transmission line connected to it.

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