Horn-based circular polarized antenna array with a compact feeding for Ka-band monopulse antenna

A pyramidal horn monopulse array is proposed for working at Ka-band with circular polarization (CP) characteristic. The array is composed of 28 elements with a 28-way waveguide power divider network. The element has a pyramidal horn with a rectangular waveguide, which is placed downside the horn. There is a 45 inclined slot cut in the wide wall of the rectangular waveguide. The inclined slot can convert the excitation into two orthogonal modes with equal amplitude, and 900 out of phase is produced due to different propagation constants of the two modes in the pyramidal horn. Therefore, the antenna can achieve CP by using a compact structure without polarizer. This paper also provides procedure of the compact power divider network for synthesizing monopulse pattern. This monopulse array has excellent performance: The simulated and measured reflection coefficients of the sum port and difference port of the array are below -15 dB, the side lobe level of array less than -27dB, and axial ratio < 3 dB in the mainlobe beamwidth. The simulated and measured results are in good agreement.