VECTOR SIGNAL ANALYZER:
The integrated vector signal analyzer (VSA) makes it possible to measure signal distortion caused by the device under test quickly and reliably
Vector signal analyzers extend the capabilities available in a spectrum analyzer. Though similar to Fourier analyzers, vector signal analyzers provide capabilities through the RF range, offering fast, high-resolution spectrum measurements, demodulation and advanced timedomain analysis. They are especially useful for characterizing complex signals such as burst, transient, or modulated signals used in communications, video, broadcast, sonar, and ultrasound imaging applications.
The vector signal analyzer is also capable of modulation analysis. Similar to Fourier analyzers, vector signal analyzers extend the capabilities of DSP through the RF range. Since both the magnitude and the phase of signals are captured, vector signal analyzers can provide a broad range of measurements including spectrum, modulation and power on baseband, IF, or RF signals. Vector or I and Q formats can be analyzed in addition to AM, FM and PM formats. Vector signal analyzers are especially useful when a broad range of measurements is required, for example, in the development of digital communication systems. A good article on VSA is available at:
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VECTOR NETWORK ANALYZER:
Network analyzers measure tranfer function characteristics of devices by applying a precise, known input signal and measuring the response output signal (automatically measuring in both directions). There are two types of network analyzers: scalar and vector. The former measure only magnitude transfer functions (spectrum analyzers can operate as scalar network analyzers with a device called a tracking generator). The latter measures both magnitude and phase and output is first s-parameters and various derived two-port parameters.
AND A GOOD ARTICLE ON THE BENFITS OF VECTOR ANAYLSIS IS AT :
https://zone.ni.com/devzone/conceptd.nsf/webmain/1FF540AF55ECA3FE86256CC6005500BA