Monopulse waveguide patch array antenna in 37 GHz band

We present a circularly polarized patch array in 37 GHz frequency, within a narrowband application (less than 1%) for signal detection. The designed array needs to have some specific requirements related to its radiation pattern (monopulse configuration to identify the input direction of a signal), circular polarization (RHCP) with an axial ratio under 3 dB, low sidelobe level in the sum pattern, and high gain. Taking into account this last requirement and the working frequency a lossless scheme is needed, and the waveguide feed provides it. The coupling mechanism from the waveguides to the radiating elements is made by inside microstrip lines. The radiating element is a modified circular patch easily manufactured on printed circuit.