This paper presents a comparison of two gain-enhancement techniques and the development of an extremely high-gain slotted waveguide antenna array (SWAA) aiming at applications in the millimeterwaves (mm-waves). The first technique utilizes pairs of grooved structures surrounding a given primary power source to improve its transmission properties, acting as secondary sources to re-radiate the surface wave energy, whereas the second is based on symmetrical wing-based reflectors. Those techniques and their combination have been applied to an SWAA based on an air-filled metallic rectangular waveguide. The proposed antenna array was designed for operation in the frequency range from 25.5 to 26.5 GHz and excited by a unique coaxial-to-waveguide transition with the TE 10 fundamental mode. These techniques enable us to enhance the gain of the array by up to 10 dB, making it comparable to those of parabolic antennas with similar size apertures. Numerical analyses of the performance-enhanced antenna arrays are presented to validate the design strategies. Experimental results of 27-and 41-slots SWAA prototypes demonstrate the potential of the wing-based reflector technique to improve its aperture efficiency over that of the grooved structures. The 41-slots SWAA prototype provides as high as 31 dBi-gain in the 26 GHz band, ranging from 30.52 to 31.13 dBi within the array impedance bandwidth. Furthermore, since the reflector structures are easily attached to and detached from the SWAA structure, the prototype has the potential to provide both sectoral and directive radiation patterns in the E-plane.INDEX TERMS 5G, antenna, grooved-structures, reflectors and slotted waveguide antenna array.

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