Difference between spectrum analyzer and network analyzer

Difference between spectrum analyzer and network analyzer

There are two main structures of spectrum analyzers: swept type and FFT. Due to the limitation of measurement frequency in FFT structure, it is generally only used for low frequency, while swept type is widely used in RF and microwave fields.

The advantages of frequency scanning to FFT are: wide frequency range, low DANL, large dynamic range, etc.

The advantages of FFT over frequency sweep are: real-time measurement

Of course, some spectrum analyzers also have FFT functions, such as PSA, general spectrum analyzer, AD acquisition of the back-end receiving signal, and then processed by DSP, which can realize the function of VSA (vector signal analyzer), such as ESA + 89601A.

Of course, the current spectrum analyzer functions can also be expanded, such as NF test, phase noise test, digital modulation test, etc., but these are usually used as options, which means additional funds are required.

The main function of a spectrum analyzer is to observe the spectrum of various modulation signals, such as amplitude modulation and frequency modulation, so as to realize the investigation of modulation degree and modulation quality. In addition, a spectrum analyzer can also measure the single-sideband phase noise in various signal sources, check the harmonic distortion in the signal, monitor the wireless signal in a certain frequency range, etc.

There are two types of network analyzers, vector and scalar. Currently, the main one is vector. That is, it can measure transmission, reflection amplitude and phase information at the same time. The network analyzer has its own signal source and receiver, but if it is understood as a combination of a signal source and a spectrum analyzer, that is. This is problematic because the current standard network analyzer can only measure linear parameters. It sweeps at the same frequency. For example, when the VNA sweeps f1, the receiver also measures the transmission and reflection of the F1 signal and calculates the S parameters again.

Of course, the functions of VNA have been expanded. Generally, VNA has a frequency option. In this way, sweep tests of frequency offset devices such as Mix can be completed. Of course, using this frequency offset, nonlinear tests of devices, such as harmonic parameter tests, can also be performed.

Another major expansion of VNA is testing differential devices. With the widespread application of differential topology, VNA has also introduced four-port VNA. However, the signal generated by VNA is not physical differential, but logical differential. It mainly completes the test of four-port network and then performs mixed S parameter conversion. The differential performance of DUT is obtained, but the four-port VNA is usually twice that of the two-port.

As for the vector network analyzer, since it has a signal generator, it can perform frequency scanning on a frequency band. If it is a single-port measurement, the excitation signal is added to the port, and the impedance or reflection situation is judged by measuring the amplitude of the signal and the phase of the network analyzer. For dual-port measurement, the transmission parameters can also be measured.