A Planar, Wideband, and Compact Hadamard Matrix for 2-D Switched Beam Antenna Array

This letter proposes a wideband two-dimensional (2-D) switched beam antenna array with single/dual/quad-lobed switched beams for direction of arrival (DOA) estimation. A planar and compact 4-order Hadamard matrix (HM) without any intersection structure works as its feeding network. The HM provides four groups of output signals with equal amplitudes and coded 0 8 /180 8 phase differences between adjacent outputs. It adopts four universal building blocks arranged planarly, each of them is realized by a 3-dB wideband quadrature coupler cascading with a 90 8 phase shifter. For demonstration, a HM prototype operating at 2.4 GHz is designed, fabricated, and measured. Its overall circuit size is 0.67 × 1.34 λg 2 and bandwidth is larger than 47.6%. Finally, a wideband 2-D switched beam antenna array is constructed by the proposed HM and magnetoelectric dipole antenna array. The 2-D single/dual/quadlobed switched beams verify its effectiveness.