What is a spectrum analyzer?Ideal for applications requiring RF testing

Infineon / Mitsubishi / Fuji / Semikron / Eupec / IXYS

What is a spectrum analyzer?Ideal for applications requiring RF testing

Posted Date: 2024-01-17

Spectrum analyzers are found in many laboratories and other areas where test instruments are needed to test and verify RF performance.

Spectrum analyzers are widely used test instruments for applications requiring RF testing: RF design, general electronic circuit design, testing; electronics manufacturing; basic service and repair, and increasingly for field installation and service.

Basic oscilloscope screen

In these applications, RF spectrum analyzers provide an effective way to understand the RF performance of a circuit, module, or system.

As the name suggests, spectrum analyzer, this type of test equipment provides information about the spectrum of a signal. Since signals at different frequencies can be seen, spurious signals as well as the spectrum of today's complex waveforms can be displayed to study whether they are within the required range at different frequencies.

With the increasing use of wireless communications, spectrum analyzers have become an important part of the RF design toolbox and are increasingly appearing in many areas of electronic circuit design.

While spectrum analyzers have traditionally been stand-alone bench test equipment, rack-mountable PXI, VXI or similar analyzers are available alongside USB spectrum analyzers. Even benchtop test instruments are able to be connected to computers so that they can be controlled by them and their results can be analyzed in greater detail.

What is a spectrum analyzer?

The most common test equipment used to display waveforms is an oscilloscope. The test instrument displays the signal in the so-called time domain, that is, the amplitude versus time. The oscilloscope is one of the core test instruments in any RF design or test laboratory and can display many waveforms and circuit performance. Modules and devices to analyze.

An oscilloscope displays the amplitude of a waveform on the vertical axis versus time on the horizontal axis - the signal is displayed in the time domain.

While this is very useful, when testing RF circuits and systems, it is useful to be able to see the spectrum of a signal - you can see where spurious signals are, the width of the signal with modulation, whether noise is being generated, etc.

When viewing the spectrum of a signal, the amplitude of the signal is displayed on the vertical axis and the frequency is displayed on the horizontal axis - the signal is displayed in the frequency domain.

By looking at signal amplitudes at different frequencies, you can measure the amplitude of these signals, find out which signals are present, etc.

Spectrum analyzers display signals in the frequency domain

In this way, the frequency of the signal can be measured and its level checked. Because many modern wireless communication signals occupy wide bandwidths, the signal bandwidth can be measured.

Therefore, a spectrum analyzer is an especially important item of test equipment for anyone who performs test and measurement of circuits and systems involving RF or RF signals. Apart from this, spectrum analyzers can also be used in various other applications including audio analysis, etc.

With the increasing use of wireless communication systems, from Wi-Fi to mobile phones and long-range wireless sensors on the Internet of Things, as well as radar, traditional radio communications and many other applications, RF design is becoming increasingly important.

Typical spectrum analyzer displaying the spectrum of an RF signal

Spectrum analyzers typically use a linear scale to represent frequency on the horizontal or x-axis, but they often use a logarithmic scale to represent amplitude on the vertical or y-axis. By using a logarithmic or decibel scale as the amplitude scale, signals with large amplitude differences can be seen.

The signals viewed on a spectrum analyzer may differ by 60dB, 70dB, or more. Using a logarithmic scale is the only way to view these signals on the same screen. For some applications it may be necessary to use a linear amplitude scale, and there is usually a switch to achieve this.

Modern spectrum analyzers are highly capable. Since most use digital technology, not only digital signal processing using Fast Fourier Analysis (FFT) is used to complete the signal processing, but also a control processor is used to control the front panel controls and display. This allows the spectrum analyzer to integrate many functions and include a large number of automated routines.

The monitor can determine the peak signal normally, displaying its frequency and power level, or it can determine the value of the signal at a specific point, or the value of the second peak, etc. These features and many more are common in today's test instruments.

What is the use of spectrum analyzer?

Today's electronic circuit design laboratories will use a large number of test instruments. Everything from a simple digital multimeter to oscilloscopes, signal generators and more.

Spectrum analyzers are particularly useful in electronics laboratories related to RF design and testing.

In these areas, they can provide a view of the signal in a way that other forms of test instrumentation cannot. This provides insight into the operation of the RF aspects of the circuit.

Spectrum analyzers can be used for a variety of tasks:

Looking at the spectrum of the signal, you can see the following items:

Modulate the overall spectrum of the signal to see if it's wide enough or too narrow etc. If it is too wide, then it may cause interference to users in adjacent channels.

Investigate for any stray or unwanted signals. These signals may cause interference to other frequencies where users are transmitting signals.

For example, find out if the signal is on the correct frequency and not in another frequency band.

Investigate general issues with signals. Often, it helps to look at the signals to understand where the problem is. For RF signals, a spectrum analyzer can prove to be the eyes of the investigator.

Sometimes, a spectrum analyzer can be used to measure power, but a power meter may be more suitable in some situations.

Frequency can sometimes be measured using a spectrum analyzer, although a frequency counter may be more suitable in some situations.

A spectrum analyzer can also be used to measure phase noise on a signal. This can be achieved if the pose noise on the spectrum analyzer local oscillator is typically 10dB higher than the pose noise of the oscillator under test. These test instruments are one of the best ways to measure phase noise, provided the spectrum analyzer local oscillator has a low enough phase noise level.

Another application for these test instruments is measuring the noise figure of items. Although the testing method does involve multiple stages, it can be performed relatively easily.

Spectrum analyzers are commonly used to make EMI and EMI (electromagnetic interference and electromagnetic compatibility) measurements. Analyzers can be used to locate the frequency and nature of signals that may be causing problems.

Although RF spectrum analyzers can be used for many RF tests, the following table summarizes the different types of test instruments used for RF testing and their typical applications.

Test Equipment Type Frequency Measurement Intensity/Amplitude Measurement Application

Power Meters NY RF power meters provide accurate total power measurements but do not provide any information about the signal spectrum.

Frequency Counter YN Frequency Counter is used to make very precise measurements of the dominant frequencies in a signal

RF spectrum analyzer YY is mainly used to display the spectrum of RF signals.Can also be used to make power and frequency measurements, but are not as accurate as specialized instruments

RF Vector Network Analyzer YY Vector Network Analyzer (VNA) measures the characteristics of RF equipment. They look at individual ports on a device and provide information about port impedance and transmission through the device.

Spectrum Analyzer Key Topics

There are several key topics related to RF spectrum analyzers and their use.

Spectrum Analyzer Types: There are several different types of spectrum analyzers that can be purchased and used. Each type has its own characteristics: performance and cost can be balanced to provide the best option for any application.

Older types were usually based on the superheterodyne principle, scanning the receiver over a frequency band and noting the output. More modern spectrum analyzers use a Fast Fourier Transform (FFT) to convert the signal from analog to digital format and then use Fourier analysis to monitor the symbols.

There is also a real-time spectrum analyzer. These instruments are based on the same concept as FFT spectrum analyzers, but these test instruments use time-overlapping samples to ensure that transients are not lost. Although more complex internally, they ensure that all signals can be seen as they need to be able to accommodate very fast and overlapping sampling. They are often crucial to solving some of the problems of today's very complex devices produced for various forms of wireless communication: 5G; Wi-Fi, etc. .

The format of the test instruments also differs. Standard box-type instruments are widely used and they provide not only manual control but also remote operation through many different interfaces including Ethernet, USB and GPIB.

Additionally, a rackmount spectrum analyzer option is available. VXI was an early rack system, but today PXI is more widely used. PXI is based on the PCI system and has been adapted for instrumentation. The controller or interface is in one slot and the rest is for the test instrument. A controller can control a system or, more commonly, be connected to a computer. This type of approach is ideal for computer control of a set of test instruments required to test a system under computer control.

Another method is to use a USB spectrum analyzer. These USB spectrum analyzers have the main functionality of an analyzer in a small box, but it connects to a PC via a USB cable so it can use display, control and control processing, and typically uses the PC's power supply to reduce costs while typically maintaining performance level. Some USB spectrum analyzers offer very high levels of performance at a very reasonable cost.

Spectrum Analyzer Specifications: While choosing an RF spectrum analyzer, it is necessary to understand its specifications and what they mean. There are many different specifications for spectrum analyzer performance, and it is necessary to understand what they mean and how they reflect into the actual performance of the test instrument.

There are many specifications to consider when choosing a spectrum analyzer. Various specifications cover every aspect of its performance. Frequency coverage: Top and bottom frequencies are obviously important, but so are frequency and amplitude accuracy. Phase noise is another critical issue, as many of these test instruments often need to be able to measure the phase noise performance of other devices, and to achieve this, their performance needs to be better than the performance of the product under test.

There are many other aspects of performance to consider when proceeding and selecting, including available facilities.

An RF spectrum analyzer is an essential test equipment for any RF engineer, whether used in RF design, general electronic circuit design, electronics manufacturing, service, repair and general RF testing.

Although spectrum analyzers are typically expensive test instruments, they are occasionally available on the second-hand market, making them accessible to enthusiastic RF experimenters and radio enthusiasts.

Beyond this, some USB spectrum analyzers offer a very high level of value because they use elements of a PC for display and input controls. Typically, most signal analysis is performed by the FPGA of the USB spectrum analyzer itself, which means a high level of functionality and performance can be obtained at a more reasonable cost.

Spectrum analyzers are also available in rack-mounted form. VXI and PXI spectrum analyzers can use these rack systems.

Spectrum analyzers are an essential item of test equipment used in RF test and RF design laboratories. They are widely used, but they are not typically found outside of these environments, although audio analyzers are used for some specific tests. .

Review Editor: Huang Fei

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