4. Conclusion

The constant emergence of new wireless systems leads to a constant demand for smarter and/or smaller antennas. This article takes an in-depth look at electrically small antennas, miniaturization techniques and antennas for cell phones.

Size reduction can be achieved by exploiting both passive and active matching circuits, or even a combination of the two. Impedance matching does not change the antenna structure; rather, it may shift its resonant frequency to lower values. Improved performance of miniature antennas over a wide bandwidth can be achieved with non-Foster element matching circuits. Non-Foster matching uses active circuit elements to cancel the reactive part of the impedance, creating a negative impedance. The difficulty with this type of circuit lies in their realization, since they are based on active elements. Although many realistic topologies can...