A Compact Ka-Band Low-Sidelobe Monopulse Antenna Array Based on Mixed Gap Waveguide and Hollow Waveguide Multilayer Feeding Network

In this article, a compact low-sidelobe 2-D monopulse antenna array has been proposed based on mixed gap waveguide (GWG)/hollow waveguide (HW) multilayer feeding network and a GWG monopulse comparator. The proposed antenna array is arranged and divided into multilayers based on the function for miniaturization and low losses. First, slot antenna elements, unequal power divider based on the GWG, and layers transition between different ridge GWGs are proposed. Then, monopulse comparator composed by groove GWG 3 dB 90° coupler and 90° phase shifter is proposed according to the network diagram for forming <inline-formula> <tex-math notation="LaTeX">$\sum $ </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">$\Delta _{\text {E}}$ </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">$\Delta _{\text {H}}$ </tex-math></inline-formula> beams. By vertically integrating the above functional elements, the compact low-sidelobe 2-D monopulse antenna array is obtained. The measurement results show its impedance fractional bandwidth (FBW) is 12.6%, antenna gain is greater than 29 dBi, and the efficiency is 35%. Moreover, the levels of the sidelobe and null depth are about −25 and −35 dB, respectively.