RF Interview Questions 4.0: S-Parameters, VNA architecture, TRL Calibration
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Microwave Network Analysis:
Introduction:
Circuits operating at low frequency, for which the circuit dimensions are small relative to the wavelength, can be treated as an interconnection of lumped passive or active components with unique voltages and currents defined at any point in the circuit.
In this case, the circuit dimensions are so small that there is negligible phase delay from one point to another. As one is aware, there is a powerful set of techniques for analyzing these low-frequency circuits.
These circuit analysis techniques can’t be directly applied to microwave circuits but can be extended to handle many microwave analysis and design problems. However, in some cases, such circuit analysis techniques are oversimplified and may lead to erroneous results.
In such cases, one must resort to a field analysis approach using Maxwell’s equations. Today, many commercially available computer aided design packages can model RF and microwave problems using both field theory analysis and network analysis.
Microwave network theory was developed in the service of radar system and component development at the MIT Radiation Lab in the 1940s.
Common RF interview questions on Microwave Network Analysis:
Explain the concept of Impedance.
What are Scattering parameters and how are they measured?
What is a Vector Network Analyzer?
How to calibrate a Vector Network Analyzer? Explain the TRL calibration method.
Now we will answer each of these questions with diagrams: