A Wideband High-Gain Planar Monopulse Array Antenna for Ka-Band Radar Applications

In this article, a wideband planar monopulse array antenna operating at Ka-band fed by the substrate integrated coaxial line (SICL) comparator network is proposed. The broadband SICL comparator is compactly deployed in the center of the feeding layer and integrated with the wideband stacked patch antennas on a multilayer printed circuit board (PCB), contributing to improved bandwidth, gain, and total efficiency. Moreover, the millimeter-wave (mmWave) front-end circuits can also be seamlessly integrated on the same board. Prototypes of $4\times4$ , $8\times8$ , $16\times16$ , and $32\times32$ monopulse array antennas are designed and fabricated. The measured results show a good agreement with the simulated ones. The $32\times32$ array antenna occupies a compact footprint of only $21.76\lambda _{0} \times 21.76\lambda _{0} \times 0.303\lambda _{0}$ while achieving an impedance bandwidth of 28.8% (28.8–38.5 GHz), a 3-dB gain bandwidth of 25% (29.25–37.6 GHz), and a peak gain of 28.6 dBi for the sum beam. The measured null depth is −56.49 dB, which indicates that excellent amplitude and phase balance is achieved by the proposed SICL comparator network. Finally, the gain variation with increasing array scales and the insertion losses of the comparator feeding networks are also investigated. The demonstrated performance merits of the proposed monopulse array antenna make it a competitive candidate for various Ka-band radar applications, such as low-cost seekers and autonomous driving.