Key indicators of network analyzers and introduction to popular brands

Vector network analyzers are a type of instrument with a wide range of uses. They can characterize S parameters, match complex impedances, and perform time domain measurements, etc. They are also one of the instruments commonly used by electronic engineers. Today, Antai Testing will explain the key technical indicators of vector network analyzers and introduce several popular brands to you. These are the brands that Antai Testing recognizes when helping customers select models. We hope to provide a reference for engineers who are selecting models.

1. Maximum frequency

The maximum frequency of a VNA refers to the highest frequency it can measure. The receiving end of a network analyzer has an analog-to-digital converter (ADC) that converts the incoming signal into a digital format. These signals can then be analyzed and displayed. However, the ADC does not have the ability to convert signals in the RF range, so the incident signal must be downconverted to its operating frequency. This operating frequency is called the intermediate frequency (IF).

2. Dynamic Range

Dynamic range refers to the range of powers over which the response of a component can be measured.

This figure shows two different ways to define dynamic range. System dynamic range is the value used for the instrument specification.

System dynamic range refers to the instrument's capabilities without using a boost amplifier and without considering the gain of the device under test. The instrument's maximum source power refers to its maximum power level, or Pref.

Receiver dynamic range refers to the dynamic range of the instrument when power amplification is used. Instead of using the source power as the maximum power level, this specification is based on the maximum power Pmax that the receiving end of the instrument can measure.

The left figure below shows a trace from a bandpass filter S21 measurement, which shows the dynamic range of the instrument. The upper limit of the trace is relatively flat, and the lower limit contains some noise. Let's look at what factors determine the shape of these boundaries.

The maximum power level of the dynamic range is determined by the upper limit of the source power level and the compression point of the receiver.

The mixers and amplifiers that make up a receiver can handle only so much power before they saturate, or reach their maximum output. When a device is in the saturation region, there is no longer a linear relationship between its input and output.

Amplifier saturation can be seen in the right-hand graph below. At input powers above 1W, the actual output (red) deviates from the ideal output (green). This phenomenon is called compression. The receiver cannot capture any device output above its compression point. This limitation on input power creates an upper limit on the dynamic range.

3. Output power

Output power reflects how much power the VNA's signal generator and tester can transmit into the device under test. It is expressed in dBm and referenced to a 50Ω impedance to match the characteristic impedance of most RF transmission lines.

High output power is useful for improving the signal-to-noise ratio of a measurement or determining the compression limits of a device under test.

Many active devices, such as amplifiers, require challenging linear and nonlinear high-power measurements that exceed the power limits of network analyzers.

4. Trace noise

Trace noise is the noise you see superimposed on the response of the device under test due to random noise in the system. It can make the signal look less smooth and even jittery. Trace noise can be eliminated by increasing the test power, reducing the bandwidth of the receiver, or taking an average.

Popular brands of vector network analyzers (in no particular order):

Keysight Technologies

Tektronix

Rohde & Schwarz (R&S)

Anritsu

Ceyear

TRANSCOM