Printed Dually Polarized Gap Waveguide and Horn Antenna based on Hard and Soft Surfaces

Polarization diversity is one of the methods used to increase channel capacity in a given spectrum. Usually, for a dually polarized system, two circuits are used each for one polarization, particularly for printed thin circuits. To carry dually polarized signals through the guiding structure made with metallic walls, the guiding structure must be at least a half wavelength width in the two planes. Conventionally, for medium gain level, horn antennas are designed by flaring metallic waveguide (square waveguide for dual polarization), which requires physical contacts to join the four walls. A flat horn can be used by flaring only two sides of the waveguide. If a standard waveguide is used, an H-plane horn is created for single linear polarization. A substrate integrated waveguide (SIW) based printed horn antennas are designed with a dielectric as a propagation medium that makes it a lossy structure. SIW must be a have half-wavelength wide to support the TE10 mode, but it will be singly polarized. Thus, for a dually polarized horn, the waveguide height and width must be at least a half wavelength, which provides an elliptic beam. Alternatively, a novel dual-polarized horn antenna is introduced to support TEM modes without having any limitations on width and height dimensions. It allows the wave to propagate in the lossless air-filled medium. To design this horn antenna, a thin dually-polarized guiding structure is proposed. To realize that, the boundary conditions at all four walls are altered. A study of different boundary conditions (PEC, PMC, Hard, Soft) is described to show that only the hard surface can support both vertical and horizontal polarization in guided structures with dimensions less than the half wavelength. Based on the concept of a hard surface, the new dually-polarized periodic structure is designed. This structure is used to develop a compact dual-polarized waveguide. To verify the polarization performance of dual-polarized waveguide, several Ortho Mode Transducers (OMT) transitions are simulated. After that, the dual-polarized waveguide is flared to design a horn antenna that supports V-TEM and H-TEM to achieve uniform amplitude distribution at the aperture of the horn antenna. With the advantage of uniform field distribution, the horn antenna achieves a narrow beamwidth with a radiation efficiency of around 80%.