High gain frequency scanning antenna using dumbbell‐shaped inclined slots and parallel plate waveguide polariser

A high gain vertically polarised travelling‐wave frequency scanning array antenna fed by a meander rectangular waveguide is presented for Ku‐band operation. The proposed antenna is used in a radar demonstrator setup to detect and monitor birds in direct proximity to the wind farms. The goal is to prevent collisions of birds with wind farms. The proposed antenna consists of 34 inclined dumbbell‐shaped radiating slots integrated with a parallel‐plate waveguide. The proposed meandered feeding structure is used to enlarge the beam scanning angle range over frequency. The dumbbell‐shaped radiating slots are employed in the narrow wall of the meandered waveguide due to the space restriction of the meandering. The parallel‐plate waveguide is used as a polarisation filter to reduce the cross‐polarisation level of the proposed antenna owing to the inclination of the radiating slots. An E‐plane horn is used to reduce the beamwidth in the elevation plane. The overall size of the antenna is 20.6λ in length and 15λ in width, where λ is the free space wavelength at 15.55 GHz. The antenna operates in the frequency range from 15.40 to 15.70 GHz. The half power beamwidth is about 4° in the azimuth plane and about 20° in the elevation plane at 15.55 GHz. The main beam of the antenna steers over frequency to cover 39° of angular range in the azimuth plane. A Taylor distribution is applied to achieve sidelobe level below −25 dB in the same plane and 26 dBi gain over the operating frequency range. The antenna array is fabricated and measured successfully to verify the proposed approach. The fabricated antenna shows an impedance matching significantly better than 10 dB in the operating frequency. The measured gain is higher than 25 dB throughout its frequency range.