Abstract: This paper describes a novel design of waveguide monopulse antenna array with open-end rectangular waveguides as radiator elements and presents the measured VSWR curve and radiation patterns respectively. The antenna element is a 90° miniaturized open-end waveguide ,which is fed from bottom by inclined slot to control the amplitude distribution of the array. The proposed antenna is easy to realize, which overcomes the disadvantages of traditional waveguide slot antenna such as complicated design and high machining precision requirement. After the analysis of the difference between the measured and simulated results, a sensitive shorting structure is replaced, a second optimized antenna element is designed and manufactured, considering two aspects of engineering realization and electrical performance. The 2.7% bandwidth (VSWR ￡ 2) and the measured radiation patterns at center frequency are all presented after experimental study, the side-lobe level for the sum pattern is less than -20 dB and the efficiency is about 45%. This proposed antenna has the similar monopulse performance with the traditional waveguide slot antenna, which presents a new design method of waveguide antenna and will have a wide application prospect on missile and satellite fields.