In order to achieve high-performance radiation in the specified direction of a broadband antenna, a wideband microstrip equiangular spiral antenna was designed. To achieve impedance matching, an exponential gradient microstrip balun structure is designed for the antenna feed section. After physical testing parameters, the results show that the antenna with exponential gradient Barron structure achieves good impedance matching and has good broadband characteristics. Its operating bandwidth is 1.74 GHz to 4.82 GHz, with a minimum return loss of -30 dB. At the same time, a flat bottom metal reflection cavity is designed to reflect back electromagnetic waves. While maintaining broadband operating characteristics, the antenna has good unidirectional radiation characteristics. The gain of the antenna in the entire operating frequency band is greater than 6 dB. Compared with traditional spiral antennas, it has the characteristics of broadband, directional, and high gain, and has certain application prospects.