Feasibility of Dual-Polarization Operation in a Slot Array by Multi-Layer Full-Corporate Waveguide Feeds

Hollow waveguide slot antennas, which have the features of low transmission loss and high cross-polarization discrimination (XPD), have been widely employed in communication and radar systems. The fabrication technique called “diffusion bonding of laminated thin metal plates” [1, 2] has been introduced in the realization of multi-layer waveguide structures with high massproductivity. The diffusion bonding is a process to realize stable surface bonding by applying diffusion motion of atom in the neighboring etched plates. It is conducted under the condition of high pressure and high temperature (~1000°C) in a protective atmosphere or vacuum. As is well known, etching of thin plates is the process of high precision around 20μm at low cost. The number of etching patterns is only five for a double-layer waveguide slot array [2]. Relatively long processing time of the diffusion bonding is not serious if a large number of antennas are processed simultaneously. Actually, waveguide slot antennas are also characterized as operating at narrowband and beam squint to disadvantage. A double-layer corporate-feed waveguide slot array antenna [3], where the feeding circuit is located in the bottom layer underneath the radiating waveguides in the top layer has been developed for wideband operation and to avoid the beam squint. A 16×16element array is designed and fabricated by diffusion bonding of laminated thin copper plates in 60 GHz band. A high gain of 32 dBi as well as a wide bandwidth of 8 % for the high efficiency of more than 80 % is achieved. Compared to reflector antennas, waveguide slot array antennas have the advantages of low profile and high XPD, and simultaneously have the disadvantages of less flexibility in beam scanning, dual-polarization operation etc. Dual-polarized waveguide slot antennas are almost absent from literature. In most previous works [4, 5], the sub-arrays with orthogonal linear polarizations are interlaced side by side. The development of dual-polarized radiating elements in common as well as corresponding exciting networks is awaited to enhance the aperture efficiency by twice. Moreover, a wider bandwidth in feeding circuit rather than the simple series feed [4] also deserves more expectations. In this paper, a multi-layer full-corporate waveguide feeding structure is proposed to excite a slot array in dual-polarization operation sharing common radiating units. The coupling cross-slot is demonstratively designed at 60 GHz, while a high isolation of more than 53 dB as well as a high XPD of more than 37 dB is realized. The structure and the principle of operation will be explained in detail.