Spectrum analyzer principle diagram

Spectrum analyzer is one of the commonly used electronic measuring instruments. Its function is to distinguish the various frequency components in the input signal and measure the frequency and power of each frequency component.

Let's take a look at the principles of traditional spectrum analyzers and the development of modern spectrum analyzers (or signal analyzers). The figure below is a block diagram of the structure of a traditional swept spectrum analyzer.

Block diagram of a traditional swept spectrum analyzer

The input signal enters the spectrum analyzer and is mixed with the local oscillator. When the mixing product is equal to the intermediate frequency, the signal is sent to the detector, which outputs the video signal. After amplification, sampling, and digitization, the vertical level of the CRT display signal is determined. The scanning oscillator controls the horizontal frequency axis of the CRT display and the local oscillator tuning synchronization. It also drives the horizontal CRT deflection and tunes the local oscillator.

The spectrum analyzer relies on the intermediate frequency filter to distinguish each frequency component, the detector measures the signal power, and the signal frequency value is obtained based on the correspondence between the local oscillator and the horizontal axis of the display.

The working principle of this scanning-tuning analyzer is just like the AM receiver in your home, except that the local oscillator of the AM receiver is not scanned, but manually tuned with a scale knob, and the sound is played with a speaker instead of a display.

The figure below is the block diagram of the latest Agilent MXA series spectrum analyzer.

Architecture of a modern spectrum analyzer/signal analyzer

MXA uses all-digital intermediate frequency and digital signal processing to perform spectrum analysis and signal vector analysis, which is the biggest difference between modern spectrum analyzers/signal analyzers and traditional spectrum analyzers. The digital processing part is equivalent to a multi-standard signal receiver, and the combination of software and hardware can meet various spectrum analysis and vector signal analysis applications.