Abstract
This paper presents a design methodology of three-dimensional (3-D) passive metallic waveguide-array lens antenna (MWALA) by implementing the Rotman lens concept (RLC) for collinear multi-beam radiations on the same angular plane. The RLC methodology extends the original concept of two-dimensional (2-D) tri-focal Rotman lens into a 3-D one in free space. Thus, the MWALA has a planar aperture facing to the radiation boresight to resemble a planar phased array of waveguide antennas and also has a curved focal surface profile (CFSP) on the opposite side to receive the illumination by the radiations of feed antennas. The three co-planar focal points are specified to define a circular focal arc (CFA) for multiple feed placement to radiate multi-beams through this MWALA. The boundary formed by the CFSP and CFA resembles the shape of Rotman lens equivalently realized in free space. In addition, the shortage of freedoms in conventional MWALA design limited to dual-focus configurations and resulting in narrow scan angles, is relaxed by adopting the phase velocities inside the waveguides as an additional freedom to realize a tri-focal configuration and broaden the scan angles of multi-beam radiation. Theoretical foundation and design guidelines are summarized with numerical and experimental examples presented to validate the feasibility.
Highlights
Design of three-dimensional (3-D) metallic waveguide-array lens antennas (MWALAs) by implementing the Rotman lens concept (RLC) [1]–[5] to radiate collinearly overlapped multi-beams is presented in this paper when the MWALAs are illuminated by the radiations of multiple feeds
This paper presents a design approach of MWALA based on a conceptual extension of Rotman lens to determine the bottom surface profiles
The 3-D Rotman lens is a virtual structure realized by free space instead of by using PCB-based substrates
Summary
Design of three-dimensional (3-D) metallic waveguide-array lens antennas (MWALAs) by implementing the Rotman lens concept (RLC) [1]–[5] to radiate collinearly overlapped multi-beams is presented in this paper when the MWALAs are illuminated by the radiations of multiple feeds. Following the procedure of RLC, the CFSP is determined by building up a set of three linear phase equations according to three designated focal points on the CFA for the 3-D Rotman lens. These three equations cannot be simultaneously solved by the conventional MWALA structures as they may only provide two freedoms. The CFCP and the related geometrical parameters of this RLC-based BFN are determined by a set of three phase equations according to the requirements of linear phase impression to excite the antenna array for three directional beam radiations These equations are built by the net phase delays of rays initially arising from the tri-focal feeds to propagate inside the substrate and reach the antenna ports of the BFN, plus the phases produced by the TLs of various lengths between the BFN’s and the actual antenna ports.
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