High-Directivity Microstrip Patch Antennas Based on TM_odd-0 Modes

High-directivity microstrip antennas are attractive for the line-of-sight communications due to their thin profile. In order to achieve a high-directive radiation pattern, the geometry of a patch operating at a TM_odd-0 mode is modified to minimize the effect of out-of-phase currents. Two high-directivity microstrip patch antennas operating at modified TM₃₀ and TM₅₀ modes are presented. They exhibit broadside radiation patterns with directivities of 15 and 18 dBi, respectively. The advantage of the proposed technique compared to an antenna array is that no feeding network is required, and thus, the design is simpler and avoids the losses caused by the feeding network. A prototype to validate the proposed technique is built, achieving a measured directivity of 14.6 dBi. The microstrip patch antenna has a total size of 3(λ/2) × 3(λ/2), and its measured bandwidth is four times that of an equivalent array of microstrip patches operating in its fundamental mode.