Accurate Vector Mixer Measurements with a Vector Network Analyzer
1 Introduction
Frequency-translating devices such as mixers and converters are fundamental building blocks of most RF and microwave communication systems. Accurately characterizing the performance of these devices is a critical factor in the design process. The frequency offset function provided by Siglent SNA series allows the source to work at the mixer's input frequency while the receiver alternates operation between the mixer’s input and output frequencies. Since phase comparison of different frequencies is meaningless, the phase characteristics of frequency conversion device cannot be obtained. This technique is called scalar mixer measurement. To obtain the phase characteristics of a mixer, we need to use vector mixer measurement techniques.2 Small Signal Model of Mixers
Since phase is a relative value, its measurement requires a reference baseline. Co-frequency devices can be directly characterized by the phase difference between the input and output signals to insert the phase shift. While mixers have different input and output frequencies, they cannot be directly compared in phase, and its phase characteristics are very much related to the operating mode, so a clear definition of the phase characteristic model of a mixer is needed before exploring its test method.The output signal of a mixer contains multiple spectrum components. Take fundamental frequency mixing as an example, the input signal of mixer be denoted as IN and the local oscillator as LO. The mathematical expression for multiplying the two signals can be described as follows:
Click to download the whole article.
