Differential Antennas: Fundamentals and Applications

Driven by the great demand for highly integrated wireless system-on-chip and system-in-package devices, there has recently been increasing interest in the research and development of differential antennas. Many studies on the design, analysis, and measurement of differential antennas have been published. This paper presents an overview of the fundamentals and applications of differential antennas. First, it compares differential to balanced and single-ended to unbalanced antennas and explains why the new terms (differential and single-ended antennas) should be adopted instead of the old terms (balanced and unbalanced antennas). Second, it addresses the quantitative relationship between a differential antenna and its single-ended counterpart, which is important and useful because the properties of either the differential or single-ended antenna can be determined from the other with a known solution. Third, it describes how differential antennas can be measured, with a special emphasis on the balun method. Fourth, it classifies differential antennas into wire, slot, microstrip, printed, and dielectric resonator antennas to better present their suitability and functionality. Fifth, it provides application examples of differential antennas from simple discrete wire to sophisticated microstrip designs. Finally, it is argued that the old paradigms of lower gains and bulkier sizes of differential antennas as compared to single-ended antennas do not always hold true; for instance, differential microstrip patch antennas can possess comparable or even smaller sizes and higher gain values than single-ended microstrip patch antennas.