Types, functions and applications of spectrum analyzers

Like network analyzers, oscilloscopes, and signal generators, spectrum analyzers are also essential RF test and measurement instruments.

Among all RF test instruments, spectrum analyzers are the most comprehensive ones, which can be fully applicable to laboratory equipment, integrated into larger RF test assemblies, used as part of mobile RF signal/interference capture applications, or even worn by wireless and cell phone tower technicians. These devices are essential for identifying and locating interference signals and measuring RF components and systems.

1. Application of spectrum analyzer

Spectrum analyzers are essentially highly specialized receivers that can be configured in a variety of ways, so they have a wide range of applications and can be used to detect and measure continuous wave (CW) and modulated RF/microwave signals. Typically, the sensing hardware and related functions of a spectrum analyzer are combined with software and control systems to achieve more powerful signal information collection and measurement. For example, some spectrum analyzers can be used to measure dynamic range, peak power, average power, peak-to-average power ratio (PAPR), and other performance measurements required in characterizing RF devices.

When using a spectrum analyzer, the most common and familiar interface is the standard frequency vs. signal power curve. Some spectrum analyzers can also plot frequency and signal power over a period of time, called a waterfall diagram, which is very useful for analyzing transient signal characteristics within that period of time. Other common spectrum analyzer interfaces include modulation/demodulation diagrams, some of which can directly display IQ data from the input signal.

Types of Spectrum Analyzers

Spectrum analyzers are also called signal analyzers. The main types are: swept spectrum analyzers (SSA), real-time spectrum analyzers (RTSA) and vector spectrum analyzers (VSA). Swept spectrum analyzers (SSA) use tuning elements to sweep along the desired frequency range. Old-fashioned swept spectrum analyzers (SSA) use analog tuning, filtering and display elements when working, while modern swept spectrum analyzers (SSA) digitize the input signal and use the fast Fourier transform (FFT) method to convert the time domain input signal to the frequency domain. Real-time spectrum analyzers (RTSA) are similar to swept spectrum analyzers (SSA), except that real-time spectrum analyzers (RTSA) use superimposed FFT when sweeping, so that signals with very short duration can be captured. Real-time spectrum analyzers (RTSA) can also be used to continuously capture signal information within a set frequency range until the limit of the real-time bandwidth is reached.

3. Connection components of spectrum analyzer

Although most of the hardware required to operate a spectrum analyzer is already built into the device (or between the analyzer and the PC for PC-driven spectrum analyzers), additional RF components are still required to connect the analyzer to the device under test (DUT), antennas, and transmission lines. These RF components usually include coaxial adapters, which are used to connect the coaxial input port of the spectrum analyzer to any device or coaxial cable. In addition, portable antennas are essential in interference hunting or signal hunting applications, and they are also very useful for external testing. Finally, when dealing with signal levels that exceed the threshold of the spectrum analyzer, an RF attenuator is required, because the built-in attenuator of the spectrum analyzer is too limited to attenuate the external input signal.