A High-Gain Single-Feed Dual-Mode Microstrip Disc Radiator

A novel high-gain circular microstrip radiator is proposed. The antenna consists of two circular discs, in a stacked configuration, designed to operate in TM11 and TM13 modes. The patches are designed, so that the resonant frequencies for both modes converge into a single frequency. It is found that by simultaneous excitation of both resonant modes, high gain and low sidelobe level (SLL) can be obtained in the radiation patterns. Excitation is done using a single coaxial feed. The fundamental working principle of the antenna is based on the superposition of radiated far fields of the TM11 and TM13 modes. At first, through a pattern synthesis, using different far field mode amplitude ratios, it is shown that the substrate dielectric constants can be selected for both layers such that it leads to low SLL. Next, for practical antenna design, the mode excitation, input impedance, and radiation properties of the TM13 mode are studied. For sound understanding and explanation, the edge voltage ratio at the aperture and mode amplitude ratio in the far field are calculated and their effects on SLL and peak directivity are discussed. Finally, the measurements results are provided in support of simulations.