Study of electrical separation in differential feed rectangular microstrip patch antennas

This paper studies the influence of the feed points on behavior of differential feed microstrip patch antennas. When the feed points are shifted from the center of the patch to the edge, higher order modes occur, for instance, TM₁₁. As a result, the imaginary part of the differential antenna impedance shifts to higher values. The electrical separation condition (ψ) of the differential feed antenna is smaller for a center feed than that for an edge feed. Several antenna prototypes with different feed points were fabricated and measured. The measurements verify our analysis.