By Doug Jorgesen
A high frequency tone or carrier is defined by two parameters: the magnitude and phase. In many applications it is required to modify the magnitude and phase of a carrier to an arbitrary state. For example, when creating a phased array antenna, the different paths need to be tuned to a specific phase and magnitude.
This function can be easily achieved in a laboratory setting by using an IQ mixer. As discussed in the blog All About Mixers as Phase Modulators, an IQ mixer provides separate paths for the in phase (I) and quadrature (Q) components of a carrier. In the IQ mixer structure, these two components are separated by an LO quadrature hybrid, then sent to independent double balanced mixers. These two mixers can be used to convert the tone, but if a DC current is applied then only the amplitude of each component will be modulated. Essentially the LO-RF isolation of each mixer is modified, which leads to decreased insertion loss with increasing current (up to the current handling limit of the mixer).