Measure Cable and Antenna Using the N9321/22C Basic Spectrum Analyzer (BSA)

Abstract

In addition to measuring the frequency power characteristics of your device or system with a spectrum analyzer, sometimes you need to evaluate the performance characteristics of antenna, RFID tags, or RF Tx modules, such as their return loss, insertion loss, and VSWR. The Keysight N9321C (9 kHz to 4 GHz) and N9322C (9 kHz to 7 GHz) basic spectrum analyzer (BSA) support those additional measurements using an optional tracking generator (Option TG4/TG7) and reflection measurement (Option RM4/RM7). The built-in bridge in the tracking generator makes the N9321/22C an easy-to-use reflection analyzer.

Introduction

A scalar reflection measurement evaluates how efficiently energy is transferred into a device and reveals the degree of mismatch between a device and a Z0 transmission line (Z0 = characteristic impedance, typically 50 Ω). Not all the energy incident upon a device can be absorbed by the device, and a portion of the energy is reflected back toward the source. We can determine the efficiency of energy transfer by comparing the incident and reflected signals. See Figure 1.

The Benefits of Using the N9321/22C BSA for Cable and Antenna Measurement

The N9321/22C BSA is a multi-use spectrum analyzer. You can easily set it up to cover reflection measurements by adding Option TG4/TG7 and Option RM4/RM7. The benefits of using this solution include:

1. Simple test setup

The built-in VSWR bridge on the tracking generator makes the connection straightforward and eliminates the need for an external bridge (Refer to Figures 2 and 3).

2. Excellent reliability and repeatability

The simple test setup reduces potential measurement error from the cable.

3. Superior reflection measurement accuracy

The N9321/22C BSA reflection measurement mode uses an open-short-load (OSL) calibration procedure, which eliminates system errors better than others that use a single calibration (open or short) procedure.

4. Simple operation

Once the OSL calibration is finished, the N9321/22C BSA is in vector network analyzer mode, therefore, you only need to control the frequency range of interest. The N9321/22C BSA allows you to read both return loss and VSWR.

Making a Reflection Measurement with the N9321/22C BSA

Three-step guide to make an accurate reflection measurement:

• Set up the spectrum analyzer’s control settings (mode, frequency, RBW, sweep time, etc)
• Calibrate the N9321/22C BSA with the Keysight N9311x-201 OSL calibrator in order to eliminate system error and temperature drift errors
• Re-connect the DUT and read the measurement result from the analyzer