Question
What three test loads are used to calibrate an RF vector network analyzer?
Answer Options
- A) 50 ohms, 75 ohms, and 90 ohms
- B) Short circuit, open circuit, and 50 ohms
- C) Short circuit, open circuit, and resonant circuit
- D) 50 ohms through 1/8 wavelength, 1/4 wavelength, and 1/2 wavelength of coaxial cable
Correct Answer: B
Explanation
A Vector Network Analyzer (VNA) is a highly complex instrument used to measure the scattering parameters (S-parameters) of an RF network. To achieve the high accuracy required for microwave work, the VNA must undergo a calibration process known as SOLT (Short, Open, Load, Thru) or OSL (Open, Short, Load) calibration.
To calibrate the analyzer’s measurement plane (the point where the device-under-test connects), the instrument measures three precisely defined reference impedances. These are a short circuit, an open circuit, and a perfect 50-ohm load (or the characteristic impedance of the system, e.g., 75 ohms). The VNA uses these three known standards to mathematically remove the effects of the test cables and adapters, shifting the measurement reference plane directly to the input of the device being measured.
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