2.3 Radiation Pattern and Directivity of a Linear Rectangular Microstrip Patch Antenna

The transmission line model, combined with the measured and computed thermal plots, suggest a model for the computation of radiation patterns of a rectangular microstrip patch antenna in the TM ₀₁ mode. The fringing fields at the edge of a microstrip antenna which radiate are centered about each edge of the antenna. This implies that the radiation would be comparable to a pair of slots centered about each radiating edge driven in phase. These slots can be viewed as equivalent to slots in a groundplane with a uniform electric field across them. This is illustrated in Figure 2-9a). In Figure 2-9b) is an FDTD thermal plot of the magnitude of the electric field distribution of a microstrip antenna cut through the plane. We can see the two radiating edges, and the fields which radiate, form a semi-circle about each edge. The electric field extends outward from each edge along the dielectric substrate about the same amount as the dielectric thickness.

Figure 2-9: a) Top view of a rectangular microstrip patch with a pair of equivalent slots located at a distance a apart. The electric fields across the slots radiate in phase. b) Side view FDTD thermal plot of the electric field for the patch analyzed in Figure 2-8 fed with a square coaxial cable. This plot demonstrates the radiating electric fields are approximately constant at each radiating edge of the patch and extend for a...