Time Domain Analysis with a CMT VNA

A Vector Network Analyzer (VNA) natively measures complex S-parameters of a device under test (DUT) in the frequency domain mode by sweeping across various frequency points. While there is an exhaustive list of measurements that can be accomplished in the standard frequency domain mode – using the advanced inverse Chirp z-transformation, the measurements can also be simultaneously analyzed in the time domain mode. This gives the added advantage where the two fundamental modes of analysis can be performed by one single instrument.

A VNA with its highly accurate vector error correction method can precisely locate the mismatches just like a traditional Time Domain Reflectometer (TDR) would. Although both instruments provide frequency and time domain using Fourier transform, they work differently in terms of the principle operation. Unlike a TDR where it sends a step or an impulse down the transmission line and compares the reflected signal with a wideband oscilloscope, a VNA uses narrowband tuned receivers to compare the swept frequency signal, thereby paving way to achieve better signal to noise ratio. Creating a higher dynamic range, which is useful for a lot of measurements, even in the time domain mode.

For an RF/Microwave engineer, time domain measurements are primarily useful in identifying a device’s behavior at specific locations. And more recently, with the increasing necessity of high-speed applications, VNAs are also gaining popularity with digital engineers for signal integrity tests.