A Broadband Low Sidelobe Waveguide Slot Monopulse Antenna Array With Reduced Structural Complexity

This paper presents a Ka-band waveguide slot monopulse antenna array featuring broadband, low sidelobe level (SLL) and reduced structural complexity. A modified 1-to-4 backed cavity is proposed to form an unequal-power 2 × 2 subarray, enabling element-level amplitude tapering and phase compensation within a three-layer metallic structure. The input-port offset in the backed cavity provides a degree of freedom for unequal-power division, while the compensation stubs mitigate the phase imbalance and maintain stable in-phase radiation. By combining the unequal-power 2 × 2 subarrays with a folded unequal-power full-corporate feeding network integrated with a planar Magic-T, the proposed 2 × 16 linear array realizes broadband monopulse radiation without introducing additional metallic layers. A prototype is fabricated and measured, achieving a 17.1% relative impedance bandwidth from 32 to 38 GHz with |S₁₁| < −10 dB. Measured results demonstrate an H-plane SLL below −20 dB and a difference-beam null depth greater than 40 dB.