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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.INDEX TERMS Antenna radiation, multi-beam radiation, Rotman lens, waveguide array lens antenna.

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This study proposes an improved method for sector nulling in the radiation pattern of rectangular phased array antennas using two different synthesis techniques; an orthogonal Discrete Fourier transform and a quasi‐orthogonal Dolph‐Tschebyscheff based technique. In traditional synthesis techniques, broad elemental beams serve as local field basis functions (FBFs) in an array. Instead, the proposed methods produce low sidelobe narrow beams as FBFs. A set of these FBFs can effectively constitute the array's radiation pattern in a confined angular region. By properly weighting these FBFs, sector pattern nulls in a designated angular range are synthesized without severely distorting the patterns outside this area. The FBFs' optimal weights can be efficiently calculated using a nonlinear minimum least squares error technique, which is later transformed into the array's elemental excitation coefficients. Along with faster convergence, this technique allows control over peak sidelobe level, null depth, and width, making it suitable for GPS anti‐jamming, 5G communications, and other applications requiring interference suppression.

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