Planar Microstrip Endfire Antenna With Multiport Feeding

Design of a planar microstrip endfire antenna with three feeding ports is presented in this letter. There are five layers in the vertical direction of the antenna, which are the radiating patches, the upper substrate, the metal ground, the bottom substrate, and the feeding microstrip lines, respectively. The patches contain the driven element and the second elements. There are four feeding points on the driven element, and each point is connected to the feeding microstrip line on the bottom layer by metal vias. Strong coupling is established by the connection between the driven and the second elements through the coupling bridges of microstip lines and metal vias. While a different port is excited, a different kind of electric field distribution is generated on the antenna. Correspondingly, a different kind of radiation pattern is obtained. Simulated and measured results show that, in the xz-plane, the antenna excited by the three ports in turn can attain a bidirectional endfire radiation pointing at +/- 80 degrees and two directional endfire radiations pointing at +/- 81 degrees, respectively.