Circular aperture antenna with spherical lens for mmWave radar level meter

This paper proposes a novel design for a circular aperture antenna using a spherical lens and absorbing material to achieve narrow beamwidth and low side lobe level (SLL) for mmWave radar level meter (RLM) applications. The proposed circular aperture antenna consists of a circular cylinder, a single medium spherical lens, a circular radiator, and a broadside-coupled stripline (BCS) feeding structure. The quadrature hybrid with the BCS structure provides 90-degree phase difference signals to the circular radiator, which is uniformly distributed across a short-distance aperture through the spherical lens, resulting in a narrowly radiating beam. The primary challenges addressed by this design include achieving narrow beamwidth (HPBW < 8°), low sidelobe level (SLL < 38 dBc at angles > 60°), and compact form factor (length < 20λ) simultaneously with cost-effective manufacturing. The most notable feature of the proposed antenna is its short length (14.5λ), made possible by using an inexpensive single-medium spherical lens, compared to the existing RLM antennas that are much longer. The developed antenna achieved a half-power beamwidth of 6.5 degrees and an SLL of −50 dBc or less above 60 degrees, confirming that the proposed circular aperture antenna is suitable for the mmWave RLM.