The trend of using metamaterials in designing microwave components
and antennas has played a great role in the past two decades. One of these
trends was the use of composite right/left-handed artificial transmission
lines for these components. On the other hand, the development of
tunable microwave components is one of the permanent demands in
the electromagnetic designer community. Mixing the advantages of
metamaterials with magnetic tunable components has opened a new
window for the development of good components. This paper reviews
different designs for tunable metamaterial-based microwave impedance
transformers. The designs illustrate different functionalities based on
the unique properties of the metamaterial composite/right-left-handed
transmission lines. The designs are supported by detailed theory and
mathematical modeling. The advantage of the presented devices is their
combined properties of compactness and nonreciprocity. Furthermore,
the devices require very low external DC magnetic bias due to their
much lower demagnetization compared to the microstrip configuration.