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Software controls the instruments and the tuners.A similar technique applies at the input by measuring the reflected power to determine the best input match. By applying a tone at the input to the load pull system and measuring the power at the output while varying the load impedance, the point of maximum output power can be determined.In the Carleton installation, the load pull uses sliding mechanical tuners (actuated by stepper motors) to synthesize different load or source impedances to the DUT.The top link below has the best introduction to load pull, but a brief explanation is presented here.Agilent: Specifying Calibration Standards for the 8510 VNA (useful for other VNAs / cal types as well).Maury Microwave: Verifying VNA Source Match Using Coaxial Offset Shorts.Maury Microwave: Verifying the Performance of VNAs.Agilent AN1287-3: Applying Error Correction to VNA Measurements.Cascade Microtech: Advanced RF Calibration Techniques.Cascade Microtech: Intro to On-Wafer Characterization at Microwave Frequencies.For information on calibration, see the following papers:.See: Maury ATS Manual: Accuracy Considerations for S-parameter Calibration. Maury highly recommends TRL calibration, however the 8720ES VNA does not support this type of calibration without option 400.Calibration standards are SOLT from the Maury 7mm cal. 7mm calibration: uses 3.5mm to 7mm adapters on the VNA cables.On-wafer calibration: uses a calibration substrate (SOLT) to remove all effects (cables, adapters, tuners, probes, etc.) up to the probe tips.There are two main VNA calibrations required for the setup at Carleton:.Agilent AN1291-1B: 10 Hints for Making Better VNA Measurements.Agilent AN1287-7: Improving VNA Measurements of Frequency-translating Devices.Agilent AN1287-4: VNA Measurements: Filter and Amplifier Examples.Agilent AN1287-2: Exploring the Architectures of VNAs.Agilent AN1287-1: Understanding the Fundamental Principles of VNAs.For information on VNAs, see the following papers:.Agilent AN1364: De-embedding and Embedding S-Parameter Networks Using a VNA.AN-95-1B.MOV - matching on the Smith Chart.AN-95-1A.MOV - conceptualization of the Smith Chart.HP AN95: S-Parameter Techniques (HP's classic paper on the topic).For information on s-parameters, see the following papers:.
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Once the VNA is calibrated it is important to move the cables as little as possible.Calibration removes the effects of cables, connectors and probes from the measurements.To obtain accurate measurements, the VNA must be calibrated.The load pull system relies on accurate s-parameter measurements of all the blocks in the system.Please familiarize yourself with the connectors.Incorrectly mating these connectors can cause PERMANENT DAMAGE.There are several types of connectors used in the load pull setup:.Determining the s-parameters of the THRU.