Microwave mixer is one of the key components of communication systems and other microwave measurement systems, it affects and determines the bandwidth and dynamic range of the system. Generally, the frequency range, conversion loss and linearity of the mixer determine the special application range of this three-port device. As the name suggests, a mixer mixes two incoming signals to produce the sum of their frequencies or the difference between them. When a mixer is used to produce an output frequency higher than the input signal (the two frequencies are added together), it is called up-conversion. When a mixer is used to produce an output frequency lower than the input signal, it is called downconversion.