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. And a 45° inclined slot cut in the wide wall of the rectangular waveguide. The inclined slot can convert the excitation into two orthogonal modes (TE10 and TE01) with equal amplitude, and 90° 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 the difference port of the array are below -15 dB, the side lobe level of array less than -27 dB, and axial ratio <3 dB in the mainlobe beamwidth. The simulated and measured results are in good agreement.
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