Microstrip-fed complementary Yagi-Uda antenna

In this study, a microstrip-fed complementary Yagi-Uda antenna backed with milled cavities is presented. This antenna is intended to radiate as near as possible to the end-fire direction while keeping a low profile and small size. The radiator and reflector elements are U-shaped slots while the director is a rectangular slot. These slots are printed on top of a very thin bendable commercial substrate. The radiator is fed by a microstrip line printed on the bottom side of the substrate. A thick metallic plate in which cavities are milled is placed below the substrate and connected by pin wires to the upper metallisation of the substrate. An S-band prototype is designed, fabricated and measured providing an operational bandwidth of 3% around 2.44 GHz, a maximum gain of about 8 dBi is achieved in the main beam which points towards 46 degrees away from the broadside direction. Finally, simulation results of array and different conformal configurations are presented demonstrating the advantages of the microstrip feeding and the thin substrate material. Bending of the antenna along H-plane and E-plane for different curvatures is evaluated.