Understanding RF - RF test and measurement equipment

RF test and measurement equipment: spectrum analyzer

The first instrument is the spectrum analyzer. The word spectrum generally refers to a range of frequencies. For the radio frequency spectrum, a special instrument, called a spectrum analyzer is used to detect and measure what kinds of signals are present at which frequencies: their powers, any modulation, etc. The most basic function of a spectrum analyzer is displaying power versus frequency, measuring where RF is present, and how much RF is present. Power is measured relative to other powers and expressed in “d-b” or decibels.

In addition to the basic power versus frequency, many spectrum analyzers can also demodulate different kinds of signals. This reaches from basic analog signals, like those used in FM radio, to complex digital signals like those used in LTE and Wi-Fi. Demodulation means extracting the information in a signal, which can also be used to tell how much error or inaccuracy is in a modulated or information-carrying signal. When a spectrum analyzer is used in this way, it’s often referred to as a signal analyzer.

RF test and measurement equipment: signal generators

RF signals come from various devices, such as cell phones, a car remote or a GPS satellite. A signal generator is used to create the different types of RF signals needed to design and test RF devices, particularly receivers. These signals can be simple, unmodulated signals, or can be complex modulated signals like those used in most wireless communications. A signal generator allows the user to control all the parameters of the signals it generates, including power, frequency, and modulation.

A common combination of test and measurement instruments is a spectrum analyzer and a signal generator. For example, if the “DUT” or device under test is an amplifier, a signal generator is used to generate a signal that is sent into the DUT. The amplified signal can then be measured and analyzed using a spectrum analyzer.

RF test and measurement equipment: network analyzer

In the RF world, a network is a device that has one or more ports, each of which can pass, reflect, and/or absorb radio frequency energy. These are usually components in a system and a cell phone has many components that can be described as a “network”. To make sure that these components are working properly to ensure the performance of the entire system, accurate, reliable, and repeatable ways to measure them are needed. Networks are tested by injecting RF into one of the ports and simultaneously measuring how much RF is reflected back from that port, and how much RF comes out of the other ports. It’s also measured how much delay is introduced by the network, and how the network changes other characteristics of the injected signal.

A network analyzer both generates and measures RF energy and is similar to the combination of a signal generator and a spectrum analyzer. Network analyzers can measure small variations or changes in signals, and sophisticated calibration routines are used to further minimize or remove error. Network analyzers are most commonly found in labs, portable network analyzers are used in the field for testing cables and antennas. Network analyzers are also referred to as vector network analyzers or V-N-As.

RF test and measurement equipment: power sensors

Power sensors are used for a simple measurement of received power. The basic function of a power sensor is reporting power as a number, such as 10.92 dBm. Power sensors are not as sophisticated as the other instruments mentioned, but they are very widely used in the RF world and can easily be found in most RF labs.

RF O-T-A testing

Most RF testing uses cables to move signals between the instrument and the DUT, or device under test. By using conducted RF, things like power levels received by the DUT can be more precisely controlled.

Some of the more recent technologies, such as 5G require over the air or O-T-A testing, where signals are radiated in and/or out of the device under test. This is mostly due to the higher frequencies used and the lack of an “RF connector” on the DUT. In this case, testing requires special shielded boxes or chambers in order to keep other RF signals from getting in and/or prevent test signals from radiating out.

Other types of RF test and measurement instruments

In addition to the four categories mentioned, there are many other types of RF test and measurement instruments.

Communications testers are a combination of a signal generator and spectrum or signal analyzer, designed to test wireless communications devices such as cell phones, Wi-Fi and Bluetooth devices. These can emulate a wireless device, access point, or base station, and allow both voice and data testing.

In EMC, or electromagnetic compatibility, electrically powered devices are tested if unintentionally RF radiating, which could interfere with other devices. For example, whether a washing machine interferes with our cell phone.

Closely related to EMC testing are amplifiers, which boost RF signal power and therefore can be used to create the high-power RF signals needed for some EMC tests.

Oscilloscopes are another category of RF test and measurement instruments, used for RF and non-RF electrical testing.