High-Impedance-Surface-Based Antenna With Two Orthogonal Radiating Modes

High-impedance surfaces (HISs) have been used as artificial magnetic conductors for low-profile dipole antennas. Usually, the desired operation has been designed using the phase-reflection simulations for normal incidence. Here, we study the properties of a mushroom-type HIS using reflection-phase calculations for oblique incidence and find two orthogonal resonant modes. An antenna based on a finite-sized HIS is designed to utilize both of these modes. Measurement results are presented for the antenna, and we report two separate modes with asymmetric radiation patterns. The first mode provides a dipole-like radiation pattern, and the second one a broadside pattern. Furthermore, the second mode can be coupled to the antenna with a proper coupling element in order to obtain a wide bandwidth. Both of the modes can be matched to 50-Ω coaxial cables, and good isolation levels between the ports are seen due to the orthogonality of the modes in the HIS.