Theory and analysis of differentially-driven microstrip antennas

This paper studies differentially-driven microstrip antennas. The theory of microstrip antennas based on the improved cavity model is expanded to analyze the input impedance and radiation characteristics of the differentially-driven microstrip antennas. The differentially-driven microstrip antennas were fabricated. Their performances were experimentally verified. Results show that the occurrence of resonance for the differentially-driven microstrip antennas also depends on the ratio of the separation ξ of the dual feeds to the free-space wavelength λ_o. When the dual feeds are located far from each other ξ/λ_o>0.1, the resonance occurs, and the input resistance at resonance is rather large. However, when the dual feeds are located near to each other ξ/λ_o<0.1, the resonance does not occur, the input resistance is quite small, and the input impedance is inductive. Compared with single-ended microstrip antennas, the differentially-driven microstrip antennas have larger resonant resistance, similar co-polar radiation patterns, and lower cross-polar radiation component.